Contact lens and methods of manufacture and fitting such lenses and computer program product

ABSTRACT

The present invention is directed to a contact lens design and methods of manufacturing, fitting and using such lenses. As an example, the contact lens may be designed to be used in a corneal refractive therapy program. The contact lens according to the invention overcomes the deficiencies of the prior art, and provides a design which allows proper fitting of a patient, whether for corrective contact lenses or for use in a corneal refractive therapy program. The ability to properly fit a patient will alleviate, at least to a great degree, corneal abrasions from poorly distributed bearing, corneal warpage from decentered lenses, edema from tight fitting lenses and discomfort from excessive lens edge standoff. The simplified design allows a novice or relatively unskilled fitter to visualize the relationship between the contact lens and cornea of a patient&#39;s eye. The design and corresponding relationship to the patient&#39;s cornea allows selection of original trial lenses and any subsequent modifications to be easily designed or corrected. The lens design also provides improved ability of a fitter to consult with a lens designer to discuss clearly the lens cornea relationship for determining of the lens design. Due to the rational design of the lenses according to the present invention, a minimal number of lens parameter increments can be identified to cover the range of common corneas. It is therefore possible to provide pre-formed lens buttons or blanks which are easily formed into a final design, thereby simplifying and speeding up the treatment process. Further, any adjustment of the lens design which may be required based upon trial fitting or the like, is easily envisioned and implemented by the fitter.

TECHNICAL FIELD

[0001] This invention relates to contact lenses and methods ofmanufacture, as well as methods for reshaping the cornea of an eye totreat visual acuity deficiencies. The invention is more particularlyrelated to non-surgical methods of reshaping the cornea. This proceduremaybe referred to as Corneal Refractive Therapy (CRT) when the therapyrelates to designing and fitting a single contact lens to reshape thecornea, and/or orthokeratology (ortho K) when referring to the use of aseries of lenses for the purpose of reshaping the cornea. The inventionfurther relates to methods of fitting contact lenses and designing suchlenses, as well as a software product for designing such lenses.

BACKGROUND OF THE INVENTION

[0002] In the treatment of visual acuity deficiencies, correction bymeans of eyeglasses or contact lenses are used by a large percentage ofthe population. Such deficiencies include patients having hyperopia orbeing far-sighted, myopia or near-sighted patients as well asastigmatisms caused by asymmetry of the patient's eye and presbyopiacaused by loss of accommodation by the crystalline lens. Although theuse of contact lenses is widespread, there are potential difficulties inproperly fitting a lens for a patient, which in turn could damage thepatient's cornea or cause discomfort. More recently, to alleviate theburden of wearing eyeglasses and/or contact lenses, surgical techniqueshave been developed for altering the shape of the patient's cornea in anattempt to correct refractive errors of the eye. Such surgicaltechniques include photorefractive keratectomy (PRK), LASIK (laserin-situ keratectomy), as well as procedures such as automated lamilarkeratectomy (ALK) or implanted corneal rings, implanted contact lenses,and radial keratotomy. These procedures are intended to surgicallymodify the curvature of the cornea to reduce or eliminate visualdefects. The popularity of such techniques has increased greatly, butstill carry risk in both the procedure itself as well as post surgicalcomplications.

[0003] Alternatives to permanent surgical procedures to alter the shapeof the cornea includes CRT and ortho-K, where a modified contact lens isapplied to the eye to alter the shape or curvature of the cornea bycompression of the corneal surface imparted by the lens. The reshapingof the cornea in orthokeratology has been practiced for many years, buttypically has required a series of lenses and an extensive period oftime to reshape the cornea. It is also typical of orthokeratologytreatment plans that the lenses used for reshaping of the cornea must becustom designed and manufactured, thereby greatly increasing the costand complicating general use of such procedures. Further,orthokeratology lenses typically have various deficiencies, particularlyrelating to properly designing a lens for a particular patient toachieve best results in the treatment process. Specifically cornealabrasions from poorly distributed bearing, corneal warpage fromdecentered lenses, edema from tight fitting lenses and discomfort fromexcessive lens edge standoff are problems associated with an improperlyfit lens. The design of orthokeratology lenses have not lent themselvesto be easily fitted for a particular patient and their needs, requiringa doctor or other practitioner to have significant skill in complexgeometric computation to properly mate the lens shape to the patientscornea and a high level of expertise in properly fitting a patient.Further, even with a high level of expertise, a lens designer many timeswill design a lens which will not work properly with a patient, and mustbe redesigned to account for the errors of the original design. Such aprocess is lengthy and increases the cost of the treatmentcorrespondingly. It would be desirable to provide a lens for cornealrefractive therapy which would allow a novice fitter to more easilyselect and arrive at a final design to simplify the fitting process.

[0004] Another deficiency of ortho-K lenses is found in the complexityof the designs, which exacerbate the fitting problems mentionedpreviously. In the fitting process, if there is an aspect of the lensdesign which is not properly fitted for the desired treatment of thepatients eye, or causes excessive discomfort to the patient, the lensmust be redesigned accordingly. Unfortunately, in an attempt to redesigna lens, a practitioner may affect other aspects of the lens due to theinterdependency between design features or may not anticipatemanufacturing variances required by the altered design. It would beworthwhile to provide a CRT lens having independent features, whichcould be easily modified if required to attain a proper fit in a simplerand more cost-effective process. It would also be desirable to providean CRT lens design which enhances the ability of a fitter and aconsultant to discuss more clearly the lens cornea relationship, toenable parameters of the lens to be easily communicated to a finishinglaboratory for forming a desired lens.

SUMMARY OF THE INVENTION

[0005] In accordance with the foregoing, it is an object of the presentinvention to provide a CRT contact lens, method of manufacturing suchlenses and methods of designing and fitting lenses and a softwareproduct for design of such a lens. The contact lens according to theinvention overcomes the deficiencies of the prior art, and provides adesign which allows proper fitting of a patient, whether for correctivecontact lenses or for use in an orthokeratology treatment program. Theability to properly fit a patient will alleviate, at least to a greatdegree, corneal abrasions from poorly distributed bearing, cornealwarpage from decentered lenses, edema from tight fitting lenses anddiscomfort from excessive lens edge standoff. The simplified designallows a novice or relatively unskilled fitter to visualize therelationship between the contact lens and cornea of a patient's eye. Thedesign and corresponding relationship to the patient's cornea allowsselection of original trial lenses and any subsequent modifications tobe easily designed or corrected. The lens design also provides improvedability of a fitter to consult with a lens designer to discuss clearlythe lens cornea relationship for determining of the lens design. Due tothe rational design of the lenses according to the present invention, aminimal number of lens parameter increments can be identified to coverthe range of common corneas. It is therefore possible to providepre-formed lens buttons or blanks which are easily formed into a finaldesign, thereby simplifying and speeding up the treatment process.Further, any adjustment of the lens design which may be required basedupon trial fitting or the like, is easily envisioned and communicated bythe fitter and fabricated by the manufacturer.

[0006] In accordance with this and other objects of the invention, thereis provided a contact lens comprising 1) a central zone having aposterior surface having a curvature determined by the correction orreshaping to be imparted to the cornea; 2) a connecting zone is providedadjacent and concentric to the central zone, the connecting zone havinga shape defined by a first generally posteriorly concave portionadjacent the central zone (this concave portion being initially oflonger radius than the central zone then becoming steeper than thecentral zone until nearly parallel to the central axis of the lens) andtransitioning to a generally posteriorly convex portion thus having theappearance of an elongated backward “S” or sigmoidal shaped curve; and3) a peripheral zone is provided adjacent and concentric to theconnecting zone, and is provided with a conoid shape. In a CRT lens, theperipheral zone is used to facilitate redistribution of the cornealtissue with the central zone by maintaining centration during treatment.The design of peripheral zone also minimizes the potential for itsextreme edge or its junction with the first annular zone to impingedirectly on the cornea, even after ultimate contact.

[0007] In another aspect, the invention provides a contact lens having acentral zone and first and second annular zones, wherein the secondannular zone is initially positioned not to engage the cornea, andshaped such that only after the majority of redistribution of cornealtissue by the central zone is accomplished will the second annular zonecontact the cornea acting to neutralize forces imparted on the cornea bythe central zone. The first annular zone connects the central zone andthe second annular zone in the contact lens.

[0008] The invention further relates to a method for altering the shapeof a patient's cornea comprising the steps of determining the presentshape of the cornea and a desired corrected shape therefore. Thereafter,imparting a force to the cornea to alter its shape by means of a contactlens comprising a central zone having a curvature corresponding to thedesired corrected shape, and first and second annular zones concentricthereto. The second annular zone is positioned relative to the corneaand shaped such that upon redistribution of corneal tissue by thecentral zone, the second annular zone will contact the cornea acting toneutralize forces imparted thereon with minimal alteration of theperipheral cornea. The first annular zone connects the central zone tothe second annular zone in the lens.

[0009] The invention also relates to a method for treating visual acuitydeficiencies by wearing a contact lens for an amount of time to modifythe shape of the cornea in a predetermined manner. In this method, thesteps of providing a lens with a central zone having a shape designed toimpart force on the cornea and an annular peripheral zone positionedrelative to the central zone and shaped to selectively contact thecornea after an amount of redistribution of the corneal tissue by theforce applied thereto. An annular connecting zone connects the centralzone with the peripheral zone.

[0010] The invention also relates to a method for fitting a contact lensincluding enabling adjustment and visualization of the effect ofadjustments on the fit of the lens to a patient's eye. The methodenables a fitting technician to be easily taught as to the parameters ofthe lens which are modifiable to allow proper fitting based upon thecharacteristics of the patient's eye, and to assess and communicate apreferred geometry based upon the patient's characteristics. As anexample, the sagittal depth of the contact lens can be directly adjustedand assessed relative to the patient's eye for proper fitting bychanging only the axial length of the connecting or first annular zoneprovided in the lens geometry, without altering the characteristics ofthe central and peripheral zones in the lens design, and withoutaltering the location of engagement of the central and second peripheralzones that had been observed with the unadjusted lens. The fitting ofthe lens may also be directed to adjusting the location of ultimateperipheral tangential contact by the conoid peripheral zone of the lensgeometry with the cornea by adjusting the angle made by the peripheralzone to the central axis of the lens. The method of fitting is alsoprovided by measuring central corneal curvature of the patient's cornea,computing the preferred corneal curvature needed to eliminate refractiveerror for a patient, and in one embodiment, determining only twoadditional parameters, connecting zone depth and peripheral zone angle.These parameters are identified by trial fitting lenses from a lens sethaving the central zone diameter, connecting zone width, lens diameterand edge profile provided with fixed dimensions. The needed parametersof connecting zone depth and peripheral zone angle may be derived byfitting lenses from such a fitting set having a fixed connecting zonedepth with a series of base curves or alternatively, the fitting set mayhave a fixed base curve and a series of connecting zone depths. Inaddition to one or another of the two sets just described, another sethaving a fixed base curve, a fixed connecting zone depth with a seriesof peripheral zone angles from which the final angle selection isderived may be provided. Alternatively for angle selection, one of orthe other of these sets may be configured to have a plurality of visibleconcentric rings, substantially allowing a determination of the lensdiameter at which substantially tangential touch occurs between the lensand the cornea thereby making it possible to compute the correct angleof the at least one peripheral zone. Alternatively, although anembodiment of the invention restricts changes to the widths of theconnecting zone and the central zone, in some cases it may be necessaryto alter the volume distribution under the connecting zone or the sizeof the treatment zone. In such cases the central and connecting zone canbe adjusted and assessed to allow proper tear flow and oxygentransmission beneath the lens by adjusting the diameter of the centralzone, the axial length of the connecting zone and/or the radial width ofthe connecting zone.

[0011] As a further aspect of the invention, there is provided acomputer program product and methods for designing and fitting a contactlens. The computer program product comprises a computer usable storagemedium having computer readable program code means embodied in themedium. The computer readable program code means comprises code,responsive to user inputs, for modeling a contact lens to have a centralzone with a curvature selected to impart force upon a patients cornea,and first and second annular zones. The second annular zone ispositioned relative to the central zone, and is modeled to have a shapeto fit the patient's eye in a predetermined manner to provide centrationor to selectively engage the cornea upon altering its shape apredetermined amount. A first annular zone is designed to connect thecentral zone to the second annular zone. There is also provided computerreadable program code for calculating cutting parameters for a latheused to produce the lens from a blank of material. There is alsoprovided a computer readable program to use observations mad with thefitting set lenses to compute the parameters most preferred for thepatient. There is also provided a computer readable program foremploying data supplied by a topographer to compute the parameters mostpreferred for the patient.

[0012] This computer program may have the following inputs: 1) Flattestkeratometry reading; 2) manifest refractive sphere error (in minuscylinder form); 3) target final refractive error; and 4) Horizontalvisible iris diameter; the fifth input varies depending on whether thefitting lenses used had variable base curves or variable connecting zonedepths. In the case of the former the input identifies the base curve ofthe lens observed to just give simultaneous apical and tangential touch,or in the case of the latter the input identifies the connecting zonedepth of the lens observed to just give simultaneous apical andtangential touch. The sixth input also depends on which fitting lens settype is used, concentric rings or variable angles. In the case of theformer the input is the diameter of tangential touch by the lens havingthe concentric rings or in the case of the latter the input identifiesthe peripheral angle observed to meet the criteria of touch diameterrelative to lens diameter.

[0013] In either configuration the program output by computation is: 1)Lens power to order, 2) Base curve to order; 3) Connecting zone depth toorder; 4) peripheral zone angle to order; and 5) overall diameter toorder.

[0014] These aspects of the invention along with other objects andadvantages thereof will become apparent upon a further reading of thedescription of the invention in conjunction with drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a front view of an embodiment of a contact lensaccording to the invention.

[0016]FIG. 2 is a cross-sectional side view of the embodiment as shownin FIG. 1.

[0017]FIG. 3 shows an enlarged side view of the central portion of thecontact lens as shown in FIG. 1.

[0018]FIGS. 4A and 4B show a partial cross-section of a lens as part ofa set of fitting lenses.

[0019]FIG. 5A shows a schematic illustration of the connecting zone inthe lens of the invention.

[0020]FIG. 5B shows an enlarged side view of the annular connecting zoneaccording to the invention.

[0021]FIG. 5C is a schematic partial cross sectional representation ofthe first annular zone or connecting zone of the invention.

[0022]FIG. 6 is a schematic diagram showing the design of theconnecting, with spherical or conic sectional curves that might be foundin a similar location in conventional ortho-K lenses.

[0023]FIG. 6A is a diagram showing the conoid peripheral zone.

[0024]FIG. 7 is a diagrammatic illustration of an edge zone in theperipheral zone of a lens according to an embodiment of the invention.

[0025] FIGS. 8A-8C show schematically the relationship between theperipheral zone and the corneal surface of a patient.

[0026] FIGS. 9-13 show the lens design for a first example of thepresent invention, and include a spreadsheet of lens parameters, a graphshowing the elevation of the lens zones from the cornea, a plot of theindividual and cumulative volumes under the lens zones, a semi-meridiancross section of the lens and a plot showing the front and back curvesin each of the zones of the lens.

[0027] FIGS. 14-18 show the lens design for a second example of thepresent invention, and include a spreadsheet of lens parameters, a graphshowing the elevation of the lens zones from the cornea, a plot of theindividual and cumulative volumes under the lens zones, a semi-meridiancross section of the lens and a plot showing the front and back curvesin each of the zones of the lens.

[0028] FIGS. 19-23 show the lens design for a third example of thepresent invention, and include a spreadsheet of lens parameters, a graphshowing the elevation of the lens zones from the cornea, a plot of theindividual and cumulative volumes under the lens zones, a semi-meridiancross section of the lens and a plot showing the front and back curvesin each of the zones of the lens.

[0029] FIGS. 24-28 show the lens design for a fourth example of thepresent invention, and include a spreadsheet of lens parameters, a graphshowing the elevation of the lens zones from the cornea, a plot of theindividual and cumulative volumes under the lens zones, a semi-meridiancross section of the lens and a plot showing the front and back curvesin each of the zones of the lens.

[0030]FIG. 29 is a partial cross section of the edge of the lens asshown in the example of FIGS. 24-28.

[0031] FIGS. 30-34 show the lens design for a fifth example of thepresent invention, and include a spreadsheet of lens parameters, a graphshowing the elevation of the lens zones from the cornea, a plot of theindividual and cumulative volumes under the lens zones, a semi-meridiancross section of the lens and a plot showing the front and back curvesin each of the zones of the lens.

[0032] FIGS. 35-39 show the lens design for a sixth example of thepresent invention, and include a spreadsheet of lens parameters, a graphshowing the elevation of the lens zones from the cornea, a plot of theindividual and cumulative volumes under the lens zones, a semi-meridiancross section of the lens and a plot showing the front and back curvesin each of the zones of the lens.

[0033]FIG. 40 shows a method of fitting a patient in an embodiment ofthe invention.

[0034]FIG. 41 shows a schematic representation of a patient's eye andthe lens according to the invention for visualizing the fittherebetween.

[0035]FIG. 42 shows a flowchart for a computer program according to anembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0036] In the following description of the invention, the contact lens,designing and fitting methods and computer program product refer to CRTlens design, but it should be understood that the lens according to theinvention could also be designed for ortho K or to simply provide visioncorrection in a manner similar to typical contact lenses. In any lensdesigned according to the principles of the invention, the lens providesbetter centration, comfort or other advantages. Referring now to FIGS. 1and 2, there is shown a first embodiment of a contact lens forpositioning on a patient's cornea for reshaping the cornea to improvevisual acuity. The lens 10 in general is dimensioned within normalranges for corneal contact lenses, with an outside diameter generallybetween 7 to 13 mm, and generally in the range between 9.5 to 12millimeters. More particularly, the diameter will normally be chosen tobe as large as possible, but no larger than the horizontal visible irisdiameter (usually 1 mm less) and to extend beyond the point of ultimatetangential contact by the peripheral zone (as will be describedhereafter) to provide edge lift at the periphery of the lens and allowrequired tear flow under the lens. The extreme peripheral edge of thelens is smoothly contoured according to the invention as will bedescribed hereafter. The desired edge lift preferably avoids excessivestandoff, typically less than 100 microns and no more than about 150microns. Typically, the lens standoff is in the range of 40-60 microns.In other ways, lens 10 is similar to other corneal contact lenses,having a cross-sectional thickness generally in the range of 0.05 to 0.5millimeters or other suitable thickness, but being uniquely variable inthickness due to the “harmonic” correspondence between the front andback surfaces of the lens as will be described in more detail hereafter,along with the ability to independently adjust the central zone andperipheral zone thickness relative to any of the other zones. The lens10 can be fabricated from any suitable contact lens material, such asfluorosilicon acrylate, silicon acrylate, polymethylmethacrylate oranother suitable material. Oxygen permeable materials are preferredparticularly when the lens is worn overnight to permit non-wear duringthe day.

[0037] The lens 10 in general comprises a lens body having a posteriorsurface 13 including a central zone 12 provided with a curvaturedetermined by the reshaping to be imparted to the cornea of a patientfor correction of visual defects. The posterior surface 13 alsocomprises a first annular zone 14 and a second annular or peripheralzone 26, each preferably being concentric with central zone 12. Thecentral zone 12 is shown in more detail in FIG. 3, and is spherical inshape in this embodiment. Alternatively, the central zone 12 could beaspherical, toric, or comprised of a combination of annular sphericaland/or aspherical zones. In the example shown in the Figs., the surfaceis spherical and is defined as having a radius of curvature R₁. Theradius of curvature, R₁, may be chosen based upon characteristics of apatients eye for which the lens 10 is being designed, and particularlyrelated to the amount of correction required. To determine therefractive error of the eye of a patient, typical refractivemeasurements may be used and/or keratometry measurements. Using akeratometer, a single point value for the radius of curvature at theapex of the patient's cornea may be measured. Thus, there may be no needfor complex corneal topography measurements, such as by use ofphotokeratoscopy or videokeratoscopy techniques, to design the lens.Selecting the design of the other zones may be accomplished by trialfitting the lens of the present invention as an example, or inconjunction with a model eye. The objective of the trial lens fitting isto discern the sagittal depth of the cornea from its apex to thediameter at which ultimate tangential touch would occur and to select anangle making tangential touch at a diameter appropriate for the diameterof the treatment lens. Additionally, for some patients, othertopographical knowledge of the cornea may be useful. Thus, if desired,the corneal topography of the eye could be determined by use ofphotokeratoscopy or videokeratoscopy techniques as an example, tofacilitate determining the required reshaping for correction of visualdefects. Generally, for most patients the diameter of tangential touchby the second peripheral zone of the lens with the cornea is beyond thediameter measured by corneal topographers. Sagittal depth of the corneamay be grossly estimated by extrapolating data from corneal topographybeyond the range of measurement. Any suitable method for determining theamount of correction required or determining the corneal topography ofthe patient may be used. The central zone 12 is also defined as having achord diameter D₁ as shown in FIG. 3. The base curve provided on theposterior surface of central zone 12, although shown as spherical, mayalso be aspherical if desired, or have such other shapes as are known tothose skilled in the art to impart the desired shape to the cornea forcorrection of visual defects such as astigmatism or presbyopia. Ingeneral, the radius of curvature R₁ of the posterior surface 13 ofcentral zone 12 is equivalent to the desired post treatment radius ofcurvature for the cornea that is undergoing reshaping. Typically, an CRTcontact lens is to be fitted such that pressures exerted upon the lensduring lens wear are transmitted to the cornea, with the corneal tissueunderlying the portion of the lens applying pressure being effectivelyredistributed in a desired manner, but this need not always be the case.For example, the central zone 12 could be designed to correct presbyopiasubsequent to lens wear by contacting and thus reshaping the centralcornea, or be designed to correct presbyopia only during lens wearwithout contacting the cornea, depending again on the needs of thepatient. The redistribution of corneal tissue causes the cornea totemporarily take on the radius of curvature of the posterior surface 13of central zone 12 to provide correction of visual defects based uponthe present topography of the patient's cornea. The intended effect ofthe CRT lens 10 is to sphericize the apical corneal cap and establish anew radius of curvature for it. In the embodiment as shown in FIGS. 1-3,the posterior surface 13 of the central zone 12 of lens 10, beingspherical, requires only the designation of the base curve and thediameter as shown in FIG. 3. Fitting observations may be computationallytranslated to peripheral parameter choices. These choices provide thatthe peripheral design elements (connector zone depth, peripheral zoneangle and overall diameter) allow apical corneal contact, promote lenscentration, avoid excessive edge standoff and avoid pretreatmentperipheral corneal engagement which would oppose pressure applied to thecorneal apex by the central zone, and possibly other characteristics.

[0038] In order to simplify fitting, as well as to allow adjustment ofthe lens design, the visualization of the lens fit to the eye, theability to teach a fitter and communicate changes in the preferred lensgeometry for a given patient, as well as the ability to assessadjustments and the fit of the lens, it is desirable to use the minimumnumber of variables describing easily visualizable geometric shapes inselecting and designing lenses. As will be seen in more detail as thelens geometry is described, the invention is directed in part to amethod of fitting a contact lens, wherein the fitter can be providedwith a lens set where the central zone 12 diameter, connecting zone 14width, lens diameter, lens optical power and edge profile have beenpredetermined by a manufacturer. The corneal curvature needed toeliminate refractive error and the central corneal curvature can bedetermined by typical refractive measurement and/or simple keratometrymeasurements, thereby enabling the lens design to be characterized byspecifying the depth of the connecting zone 14 and the angle of theperipheral zone 26 relative to the central axis of the lens 10.Minimizing the number of variables, as well as enabling adjustment ofthese variables without impacting the design or function of the otherzones, provides unique and extremely powerful fitting capabilities. Asan example, in this manner, the fitter may be provided with a set offitting lenses having a fixed depth for the connecting zone 14, with aseries of base curves for the central zone 12 or with a set of fittinglenses with fixed base curve an a series of connecting zone depths todetermine sagittal depth of the cornea from its apex to the point oftangency between the cornea and the second peripheral zone. Similarly,the fitter could be provided with a lens set with the sagittal depth ofthe base curve and connecting zone 14 fixed, by necessity having a fixedsagittal depth greater than normal corneas, and the angle of theperipheral zone 26 varied in a series to determine the desiredrelationship between these zones. The set of fitting lenses may beconfigured to have a plurality of visible concentric rings 27 on eitherthe posterior surface 13 as shown in FIG. 4A or the anterior surface 15as seen in FIG. 4B, allowing accurate determination of the lens diameterat which substantially tangential touch occurs between the lens and thecornea to determine the angle of the at least one peripheral zone. Inthe embodiment of FIG. 4, the rings 27 are formed during the manufactureof the lens by lathe, such as by forming grooves in the surface 13 or15. In the fitting procedure, fluoroscene may be used to assess therelationship of the lens to the cornea. The formation of the rings 27 asgrooves allows fluoroscene to accumulate slightly within the grooves,such that the fluoroscene highlights the ring allowing easier viewing ofthe lens diameter at which substantially tangential touch occurs betweenthe lens and the cornea. Alternatively, the visible rings may be formedin any other suitable manner, such as by laser etching, printing,embossing or any other suitable approach. The final lens design can thenbe selected by simple computation of the angle. Table 1 as followsillustrates the fitting sets contemplated according to the invention.TABLE 1 Plurality of rings on some or Connector Peripheral zone all ofthe set Set # Base Curve Depth angle lenses 1 V F F N 2 F V F N 3 F F VN 4 V F N Y 5 F V N Y 6 F F V Y

[0039] Fitting may be performed using set 1 with set 3, or set 2 withset 3, or with set 4 alone or set 5 alone, or though it may be slightlyredundant set 4 or set 5 with set 6. Further, although the descriptionabove relates to determining certain parameters of the lens design, ifdesired, the other variables in the lens design of the invention couldalso be adjusted if desired, but limiting the number of variables whichare adjusted in the fitting process may provide significant advantages.

[0040] For example, it has been observed that the flexibility of therest of the design features of the lens according to the presentinvention make it extremely rare that a diameter of the central zoneother than 6 mm will be required, such that this possible variable maybe held constant while allowing a fitter to properly design anappropriate lens for a given patient the same time in cases of patientswith high refractive error, low corneal eccentricity, hyperopia,narrowing this diameter and expanding the connecting zone width canavoid deep tear zones under the lens that might cause bubbles as will bedescribed in more detail hereafter. Thus, it is possible to provide alens design with design variables minimized, and yet to allow suitabledesigns for such rare cases as this are enabled. The variables which arepossibly modified to achieve particular characteristics are available tothe fitter, but also may be held constant for a variety of lens designsto simplify the fitting process. In this example, both variables areexcluded from those used in normal fitting. The benefit to excludingdesign variables may outweigh their utility for many lens designs, andagain simplifies the design and fitting process. As an example, thedesign may accommodate nearly every patient using only four variables,with correction provided for nearly any eye. These variables include thebase curve, connecting zone depth, peripheral zone angle and overalldiameter. Two of these (Base curve and Diameter) are so firmly dictatedby needed correction, corneal curvature, and HVID, that they can be inmost cases fixed for a patient from records of normal eye exams. Hence,the proper fitting and design of the lens may require selection of onlytwo variables (connector depth and peripheral zone angle) and these areeasily determined, visualized and discussed between fitter andmanufacturer or consultant.

[0041] Thus, the design of the central zone 12 is simple and easilyconfigured to produce the desired reshaping of the cornea based upon thepatients measured characteristics. In general, the base curve isgenerally determined by those skilled in the art of corneal refractivetherapy at approximately 0.2 millimeters greater in radius of curvaturethan the present corneal shape, for each diopter of myopia that is to becorrected. Other visual defects may require different configurations toresult in the desired reshaping. Based upon typical patient populations,and refractive errors generally found in human eyes, the radius ofcurvature R₁ may be in the range from 5 millimeters to 12 millimeters,or more typically in the range from 6.8 millimeters to 10 millimetersradius.

[0042] The other parameter of the central zone 12 relating to chorddiameter D₁ is generally fixed at 6 mm, but in cases where it isnecessary to change this variable, it is determined by correlation tothe full pupil diameter of the patient, as measured under darkconditions. Such a design rule is not required in the present invention,and it may be easier to achieve large visual defect correction withsmaller diameter central zones 12, and thus the relationship of thechord diameter D₁ to the pupil diameter may vary. In a particularsituation, such as hyperopia or very high myopic corrections, such asabove 6 diopters, it may be acceptable to achieve the visual defectcorrection desired, to use smaller diameter central zones 12. This stillmay be acceptable even though under low lighting conditions, some flareor visual aberrations may be experienced. In general, the chord diameterD₁ is in the range from 2 to 10 millimeters, and more typically 3.5millimeters to 8.5 millimeters. Thus, once the corneal characteristicsand/or topography of a patient is determined, the design of the centralzone 12 may be configured to impart the desired amount of pressure tothe cornea for reshaping and redistribution of corneal tissue. Thus, theposterior surface 13 of central zone 12 is designed with particularattributes, while the characteristics of the anterior surface 15 ofcentral zone 12 are of less significance. The front surface 15 of thelens 10 could therefore be configured to be similar to the geometry ofstandard contact lenses with or without lenticulation. As examples, theanterior or front surface 15 of lens 10 may be configured fromcontiguous spherical surfaces, contiguous aspherical surfaces, toricsurfaces or combinations thereof. It is also possible and may bepreferable to design the front surface of the lens 10 to mirror or besubstantially the same shape as the posterior or back surface 13 usingidentical design techniques. In the embodiment as shown in FIGS. 1-2,The anterior surface 15 of the lens 10 is made to mirror the backsurface, such that the anterior surface 15 exactly parallels theposterior counterparts of the lens with equal spacing between anteriorand posterior surfaces from the center to the peripheral edge of thelens 10. At the same time, it is also possible to design the frontsurface to mirror the back surface, but to do so with different spacingbetween the surfaces from the center to the peripheral edge of the lensas will be described in more detail with respect to an alternativeembodiment.

[0043] It may also be desirable to impart the lens 10 with a desiredoptical power based upon the patient's vision characteristics. In thisregard, the anterior surface 15 may be configured in combination withthe computed posterior base curve of lens 10 to impart the desiredoptical power to lens 10. It is however normally true that the basecurve which will yield the intended correction compensates fully for anynecessary optical correction needed by the patient thus the opticalpower for all lenses offered can be set a single value near plano.Typically a base curve which would provide a correction slightly greaterthan required is employed and a power just slightly deviating from planoto compensate is provided in the lenses.

[0044] Turning now to FIG. 5A, a schematic illustration of the annularconnecting zone 14 is shown. The connecting zone 14 is adjacent andconcentric to the central zone 12, and in general is designed to have asigmoidal configuration, or the shape of an elongated “S” which isrotated circumferentially about central axis 15 through space at aradius R₂ associated with the middle of the sigmoidal form or transitionfrom a concave curvature to a convex curvature in the connecting zone14. The connecting zone 14 is a surface of rotation about the centralaxis of the lens 10, with a beginning point defined as a circlecircumscribed by the upper limit of the rotated sigmoidal shape having adiameter D₁, at 16, and terminating at a bottom point defined as acircle with a diameter D₂ circumscribed at the bottom of the rotatedsigmoidal curve at 18. The connecting zone 14 has a depth Z₁ equal tothe distance from the plane containing the upper circumscribed circle at16 and the plane containing the lower circumscribed circle at 18,measured parallel to the central axis. The end points of the connectingzone 14 (associated with circles 16 and 18) represent junctions to thecentral zone 12 and peripheral zone 26 respectively. As previouslymentioned, the anterior surface 15 of the lens 10 may be made to mirrorthe posterior surface, such that the location of junction points, whichmay be referred to as J1 and J2, are selected by translating radiallyfrom the analogous junctions on the posterior surface. The translationof J1 and J2 are individually chosen and determine the separation of theanterior and posterior surfaces and along with the front curve radiusand peripheral zone angle define the equations for the profile of theanterior connecting zone.

[0045] Turning to FIG. 5B, the design of the connecting zone 14 may bebetter understood with reference to a semi-meridian sectioncorresponding to the zone 14, inscribed within a rectangle 20, and howit may be designed. The characteristics of connecting zone do not alterthose of the central zone 12 or the second annular zone 26, and thus alens designer or fitter can design the dimensions of the inscribingrectangle independently and adjust as necessary without affecting thedesign of adjacent zones. As should be understood with reference to FIG.2, the connecting zone may be designed such that connecting zone 14smoothly joins the central zone 12 at the beginning point 16,corresponding to top left of rectangle 20. Similarly, the connectingzone 14 may be made to smoothly join the peripheral or second annularzone 26 at point 18, at the bottom right corner of the rectangle 20. Theprimary design consideration for the connecting zone 14 relates todefining the posterior surface 13 of zone 14 to begin at a pointcoinciding in space with the periphery of the posterior surface of thecentral zone 12, and terminating at a point in space where the posteriorsurface of the peripheral zone 26 begins. In designing lens 10, thedesign of central zone 12 will dictate the beginning point 16 and theslope associated with the connecting zone 14 at this point. Once thisposition and slope are located on a meridian section of the posteriorsurface of lens 10, the width and length of the imaginary rectangle 20may then be set such that connecting zone 14 terminates at position 18corresponding with the beginning of the posterior surface of theperipheral zone 26 to be described hereafter. Furthermore the slope ofthe posterior surface second annular zone 26 dictates the slope ofconnecting zone 14 at position 18. The design of the meridional profileof connecting zone 14 thus may be defined or described by its axiallength and horizontal width. Changes to the shape of the sigmoidal curvetherefore only relate to the location in space of the central zone 12and peripheral zone 26 and their slopes at the points of theirconnection to the sigmoidal curve, but do not define or reflect upon theshape of these zones, and any design parameters for these zones would beacceptable. In this way, the design of the connecting zone 14 allows afitter or lens designer to freely determine the location of the centralzone 12 relative to the peripheral zone 26, with the connecting zone 14then matched to correspond to such locations.

[0046] The design of the connecting zone 14, being a sigmoidal curve inthis embodiment, also assures the maximum “void space” geometry impartedby the sigmoidal shape of the curve as it relates to positioning on thecornea of a patient. Additionally, providing the ability to design theconnecting zone 14 based upon the beginning and ending point 16 and 18respectively, allows the fitter to easily visualize this element of lens10 as a simple rectangle and ultimately easily visualize any changesmade in the design of this zone. The ability to more easily visualizehow changes in the design will impact proper fitting to the patients eyeand cornea, makes it easier to properly select parameters to achievegood fit more simply and efficiently. As the characteristics and designparameters of the connecting zone 14 are independent of the designparameters of central zone 12 or peripheral zone 26, judgement aboutdesign parameters of the connecting zone 14 are not complicated bypossible effects on the shapes or function of the other zones. In thepreferred embodiment, the design parameters of the connecting zone 14are desired to only affect the relative location in space of the otherzones 12 and 26.

[0047] In order to achieve comfort in wearing the lens 10, it is also afeature of the embodiment as shown in the Figs., that the connectingzone 14 be designed such that the slope of the sigmoidal curve at thepoints of intersection 16 and 18 with the central zone 12 and peripheralzone 26 respectively, be substantially or exactly matched to the slopesexhibited at these locations in the zones 12 and 26. The meridionalprofile of the connecting zone is thus shaped to substantially match theslopes of the central zone 12 and peripheral zone 26 on adjacent sides.The matching of the slopes of the sigmoidal curve at the points ofintersection 16 and 18 eliminates the need for any curve blending ormanual curve fitting between independent, non-continuous surfaces as inthe present invention. Such curve blending if accomplished by means ofpolishing imparts an unknown and indescribable and irreproducible shapeto this important region of the lens and may well affect to opticalquality originally imparted to the central zone by precise lathing. Ifblending is accomplished by manual curve fitting it is not possible toautomatically compute a lens design for a particular eye but ratherrequires a designer to make unique choices for every individual greatlyslowing the delivery and increasing the cost of the lens. Further, thesigmoidal shape of the posterior surface of connecting zone 14, and thematching of the slope to that of central zone 12 at 16, tends to createthe desired void space between the lens posterior surface and thepretreatment cornea, at the position of surface 14 adjacent central zone12. The void space between the posterior surface of the lens and thepretreatment cornea is initially filled with tears and allowsredistribution of corneal tissue therein. In the present invention, theconnecting zone 14 is designed to provide a desired amount of void spaceat the desired location.

[0048] In prior art orthokeratology lens designs, the use of “reversecurves”, several indicated by reference numeral 22 in FIG. 5C can createtoo much void volume at this location, leading to bubbles between thelens and cornea, or too little room or void space for properdisplacement of corneal tissue. Further, it should be noted that such“reverse” curves require at least a radius and origin be specifiedbefore the location of the upper left and lower right corners can becomputed. The difficulty of this computation and the consequent latheset up preclude most fitters and lab operators from defining theselocations except by trial and error, and that the sharp junctionscreated require such intense polishing that even if the intendedlocations were designated they could not be guaranteed or located in thefinal product. Providing rationally spaced continuum of lenses usingsuch “reverse curves” to meet the biodiversity of human corneas cannotbe accomplished without the use of nearly intractable parameter spacingrelationships and is so difficult that manufacturers are forced to offera restricted range of lenses whose parameters give little insight intothe fitting characteristics and no guidance on how to improve amisfitting lens. The sigmoidal curve design of the connecting zone 14according to the present invention, provides a majority of the voidvolume at the location it is needed near junction 16, while allowingmatching slopes to be attained to avoid curve blending. Any use of“reverse curves” or radial arcs 22 would at best distribute any voidvolume uniformly throughout the reverse zone which is not optimum. Basedupon the possible creation of bubbles or the like, the volume createdbetween the lens and the cornea must be considered, and would limit thechoice of reverse arcs available for use. Thus, the sigmoidal curvedesign according to the present invention provides the desiredattributes without limiting the designer as the use of reverse arcswould. Further, since the sigmoidal curve is mathematically defined (seebelow) by the choice of the depth (and possibly the width) of thedefining rectangle 20, this eliminates any need for the designer toparticipate in its designation beyond specifying the rectangle's depthwhile being assured it is of optimum ultimate configuration. The priorart use of reverse curves has also taught that such reverse curves areof shorter radius than the base curve or other adjacent arcs in theortho-K lens design, such as in alignment or anchor zone arcs at theperiphery of the lens. In the present invention, the sigmoidal curvedesign is not limited in this respect, the connecting zone 14 may beprovided with effectively flatter geometry's than the adjacent centralzone over a portion of its traverse. Additionally, the computedmeridional profiles of the zones 10, 12 and 26 may be different atdifferent angles of rotation about the lens central axis allowingnon-rotationally symmetric designs. And such non-rotationally symmetricdesigns are easily visualized in each meridian in the same manner as isused for one meridian in a rotationally symmetric design. Moderncomputer controlled lathes can easily cut flatter radii in this zone asrequired and the variable curvatures in non-rotationally symmetricdesigns. Reverse curves 22 as presently practiced (steeper than thecentral base curve with origin on the central axis) present aparticularly undesirable difficulty. Whenever such curves are altered toachieve greater sagittal depth in a particular zone, the diameter atwhich the desired sagittal depth is achieved varies with the steeperradius chosen. This diameter shift then alters the entire spatiallocation of all structures peripheral to the “reverse zone”. Although a“reverse curve” 22 could conceivably be provided with a flatter radiusby moving its origin away from the central axis of the lens this wouldnot improve the ability to predict and visualize the result of such achange on peripheral structures, avoid the creation of junctions whichrequire manual polishing and curve blending, nor would it improve tearfilm distribution in the zone. The mathematically described sigmoidalshaped curve of the connecting zone 14 alleviates these problems andsimplifies design, fitting and manufacture of the lens.

[0049] The posterior surface 13 of the connecting zone 14 is determinedmathematically once various parameters are measured or determined for agiven patient's condition and the desired reshaping to be imparted tothe cornea. Again, it is desired that the connecting zone 14 interact toproperly position the peripheral zone 26 at a desired position relativeto the central zone 12, as will be hereinafter further described. Thus,the inputs for determining mathematically the curve in the connectingzone 14 will include the base curve of the central zone 12, which againmay be spherical and defined by a radius (r_(B)) as well as the slope(M) of the peripheral zone 26. The connecting zone may further bedefined by inputs including the length or “depth” of the sigmoidal curve(L), the radial distance from the center of the lens to the base curvejunction with the sigmoidal curve (J₁), the radial distance from thecenter of the lens to the junction of the sigmoidal curve with theperipheral zone, and the width of the sigmoidal curve (W) computed bysubtracting (J₂) from (J₁). In this embodiment, the equation for thesigmoidal curve is

y _(s) :=A·x ³ +B·x ² +C·x+D  (Eq. 1)

[0050] Using the above inputs, various intermediate results may then bedetermined to yield a design of the lens which can be visualized withrespect to fitting properly for the patients eye and treatment desired,allowing the fitter to more easily vary certain parameters to adjust andproperly fit the lens. As each zone of lens 10 is a surface of rotation,the lens design may be visualized with respect to a transmeridiansection, such as shown in the example of FIG. 12. The embodiment shownin FIG. 12 shows the thickness of the lens 10 varying from center toedge. For a particular patient, a designer may prefer to provide thecentral zone 12 having mirrored front and back surfaces, but thin, andthe peripheral zone 26 mirrored but thicker. In such an embodiment, thetransition takes place in the connector zone 14, which mirrors butgradually changes thickness. Using the above information, the Y valuefor the junction (J₁) between the central zone 12 and connecting zone 14is defined by the equation $\begin{matrix}{y_{j\quad 1}:=\sqrt{r_{b}^{2} - J_{1}^{2}}} & \left( {{Eq}.\quad 2} \right)\end{matrix}$

[0051] The X value for the junction (J₂) between the connecting zone 14and peripheral zone 26 is defined by the equation

x _(j2) :=J ₁ +W  (Eq. 3)

[0052] While the Y value for the junction J₂ is defined by the equation

y _(j2) :=y _(j1) −L  (Eq.4)

[0053] With these values in hand one can compute the coefficients A, B,C, D for the equation of the sigmoidal curve in this same coordinatesystem.

[0054] The values for the coefficients A, B, C and D of equation 1 aredefined by equations 5-8 as follows: $\begin{matrix}{A:=\frac{\begin{matrix}\begin{matrix}\begin{matrix}{- \left\lbrack {{\frac{- 1}{\left( {{2 \cdot J_{1}} - {2 \cdot x_{j\quad 2}}} \right)} \cdot M} -} \right.} \\{{\frac{1}{\left\lbrack {\left( {{2 \cdot J_{1}} - {2 \cdot x_{j\quad 2}}} \right) \cdot \sqrt{r_{b}^{2} - J_{1}^{2}}} \right\rbrack} \cdot J_{1}} +} \\{{\frac{1}{\left( {J_{1}^{2} - {2 \cdot J_{1} \cdot x_{j\quad 2}} + x_{j\quad 2}^{2}} \right)} \cdot J_{1} \cdot M} +}\end{matrix} \\{{\frac{1}{\left( {J_{1}^{2} - {2 \cdot J_{1} \cdot x_{j\quad 2}} + x_{j\quad 2}^{2}} \right)} \cdot y_{j\quad 2}} -}\end{matrix} \\{{\frac{1}{\left( {J_{1}^{2} - {2 \cdot J_{1} \cdot x_{j\quad 2}} + x_{j\quad 2}^{2}} \right)} \cdot x_{j\quad 2} \cdot M} -} \\\left. {\frac{1}{\left( {J_{1}^{2} - {2 \cdot J_{1} \cdot x_{j\quad 2}} + x_{j\quad 2}^{2}} \right)} \cdot \sqrt{r_{b}^{2} - J_{1}^{2}}} \right\rbrack\end{matrix}}{\begin{matrix}\left\lbrack {{\frac{- 3}{\left( {{2 \cdot J_{1}} - {2 \cdot x_{j\quad 2}}} \right)} \cdot J_{1}^{2}} + {\frac{3}{\left( {{2 \cdot J_{1}} - {2 \cdot x_{j\quad 2}}} \right)} \cdot x_{j\quad 2}^{2}} +} \right. \\{{\frac{1}{\left( {J_{1}^{2} - {2 \cdot J_{1} \cdot x_{j\quad 2}} + x_{j\quad 2}^{2}} \right)} \cdot J_{1}^{3}} - {\frac{3}{\left( {J_{1}^{2} - {2 \cdot J_{1} \cdot x_{j\quad 2}} + x_{j\quad 2}^{2}} \right)} \cdot}} \\{{J_{1} \cdot x_{j\quad 2}^{2}} + {\frac{2}{\left( {J_{1}^{2} - {2 \cdot J_{1} \cdot x_{j\quad 2}} + x_{j\quad 2}^{2}} \right)} \cdot x_{j\quad 2}^{3}}} \\{{B:=\frac{\begin{matrix}{- \left( {{A \cdot J_{1}^{3}} - {3 \cdot J_{1} \cdot A \cdot x_{j\quad 2}^{2}} + {J_{1} \cdot M} + y_{j\quad 2} + {2 \cdot A \cdot x_{j\quad 2}^{3}} -} \right.} \\\left. {{x_{j\quad 2} \cdot M} - \sqrt{r_{b}^{2} - J_{1}^{2}}} \right)\end{matrix}}{\left( {J_{1}^{2} - {2 \cdot J_{1} \cdot x_{j\quad 2}} + x_{j\quad 2}^{2}} \right)}}}\end{matrix}}} & \left( {{Eq}.\quad 6} \right)\end{matrix}$

 C:=−3·A·x _(j2) ²−2·B·x _(j2) +M  (Eq. 7)

D:=y _(j2)+2·A·x _(j2) ³ +B·x _(j2) ² −x _(j2) ·M  (Eq. 8)

[0055] Inserting these values of A, B, C, D into Eq. 1 for the sigmoidalcurve and solving the equation over the range of x values from the firstjunction J1 to the second junction J2 yields the location of all pointsalong the curve in coordinates usable by modem computer controlledlathes such as the Optoform 50. Again the posterior surface 13 isdefined to have particular attributes, while the design of the anteriorsurface can mirror the posterior shape or may be shaped as in a typicalcontact lens. Specifically the relationship of a mirrored anteriorsurface is easily determined by locating the corners of the anteriorsigmoid defining rectangle in reference to those of the posteriorsigmoid defining rectangle. The anterior peripheral zone departs fromthe lower corner of the anterior defining rectangle with the same slopeas its posterior counterpart and thus remains parallel, at least untilthe edge zone of the peripheral zone 26 is reached, which may includeedge contour characteristics, as will be hereinafter described in moredetail. The anterior central zone departs from the upper corner of therectangle with the radius of curvature required to yield the appropriatelens power. Since this power is usually near plano in CRT (the tear lensgives the necessary power correction), the thickness at the startingpoint essentially equals that at the lens center thus placing noconstraint on the lens design when selecting the relationship betweenthe posterior and anterior defining rectangles with following examplesindicating this relationship as being variable.

[0056] Turning now to FIG. 6, a peripheral or landing zone 26 accordingto an embodiment of the invention is shown in more detail. Theperipheral zone 26 in general is a second annular zone adjacent andconcentric to the first annular or connecting zone 14, and thereby isconnected to the base curve 12 by means of the connecting zone 14. Theperipheral zone in this embodiment is formed as a truncated conoid whichmay be uncurved over at least a substantial portion thereof. The conoidmay be defined by the diameter of the upper limit of the truncatedconoid, being D₂, corresponding to the diameter of the bottom limit ofthe rotated sigmoidal curve forming the connecting zone 14. Theperipheral zone 26 may further be defined by the diameter of a bottomlimit of the truncated conoid at D₃. The angle that the interior orposterior surface of the conoid makes with a plane containing thecentral axis of lens 10 may be defined as the angle of the conoid, whichis chosen by the lens designer or fitter. The relationship of themeridional profile of the peripheral zone 26 to the meridional profileof the connecting zone 14 may thus be described by the angle themeridional profile of the peripheral zone 26 makes with the a lineperpendicular to the central axis of the lens 10. In the design of theperipheral zone 26, the proper design for a given patient's cornea andthe amount of redistribution of corneal tissue which is desired by theCRT treatment, will in turn dictate relatively precisely the design ofthe peripheral zone 26. The meridional profile of the peripheral zone 26may be described by the angle it makes with a line perpendicular to thecentral axis of the lens, its curvature and its extension from thecentral axis of lens 10. The peripheral zone 26 is again separate andindependent from the central zone 12 and is joined by means ofconnecting zone 14, and altering its design in general does not effectthe design shape or location of the central zone. At the same time,depending upon the characteristics of the central zone 12, theperipheral zone is designed to work in cooperation therewith in aparticular manner in an embodiment of the lens.

[0057] In a properly fit lens at the beginning of a CRT treatmentprocedure, the central zone 12 is designed to contact the cornea at itsapex, and impart a desired amount of pressure on the cornea dependingupon the amount of correction desired. Similarly, the length of theconnecting zone 14, as represented by the length of the imaginaryrectangle as shown in FIG. 5B, as well as the angle of the truncatedconoid forming the peripheral zone 26, are selected such that theperipheral zone 26 is generally elevated above the peripheral cornealsurface a desired amount. The amount of elevation is generally selectedsuch that the peripheral zone 26 does not engage the cornea until thecentral cornea has been sufficiently redistributed to yield the desiredfinal corneal shape or change in the spherical radius of the cornea.Generally, about 3-7 microns of elevation above the cornea at thetangent point for every diopter of correction sought may be acceptable.It should also be recalled that there is a thin layer of tear (5-6microns deep) which is believed to be non-displaceable from the cornealsurface even by CRT pressures. As corneal tissue is redistributed, andat a later point in the progression of the process, the design of theperipheral zone 26 tangentially engages the curved cornea in apredetermined manner, for example approximately half way between thelens edge and J2 or slightly nearer the lens edge. By selecting theextension of the peripheral zone and its angle, the fitter is able toplace the location of the tangential touch at the greatest cornealdiameter possible. Due to the greater slope of the cornea at the largerchord diameters relative to the central cornea, the ratio of approach ofthe lens surface to the cornea at the periphery is only a fraction ofthat observed at the corneal center. Employing the widest diameterpossible for the ultimate tangential touch allows the elevation of thelens peripherally to be at a minimum relative to the displacementnecessary centrally for refractive correction. Having minimized theperipheral elevation improves lens comfort and centration thus allowinggreater consumer satisfaction and larger corrections. As furtherdistribution of corneal tissue occurs, and the engagement with theperipheral zone 26 increases, the compressive force of the lens on thecornea is borne in a progressive amount by the peripheral zone spreadingequally in both directions from the original point of tangential contact26, until the counteracting force imparted on the cornea by theperipheral zone 26 grows to effectively neutralize the centralcompressive forces imparted by the base curve 12. In this manner, anequilibrium corneal shape is established, with the peripheral zone 26contributing to the equilibrium achieved while assuring that neither thelens edge nor the connecting zone can dig into the cornea.

[0058] In rare cases, the desired correction to be imparted to thecorneal shape is significant, such that to achieve the full desiredcorrection, the pre-correction elevation of the peripheral zone 26 wouldbe so great that wearing the lens would create discomfort, or lead todislocation or decentering of the lens from the desired location on thecornea. In such an instance, the correction imparted by the lens 10 maybe performed in step-wise (orthokeratological) fashion, with each steprequiring a lens of a similar design to that described, but designed foronly partial correction of the corneal shape before equilibrium isachieved by means of the peripheral zone 26. Subsequent lenses in thestep-wise series would thereafter take up where the preceding lensterminated in terms of redistribution of corneal tissue, to continue theprocess. The step-wise approach would continue until the desiredcorrection was fully achieved. In such a process, parameters ofsubsequent lenses in the step-wise series could in effect remain thesame except for shortening the length of the sigmoidal curve (within itsimaginary rectangle) as described with reference to FIGS. 5A and 5B, toin turn provide the desired pre-correction elevation of the peripheralzone 26 relative to the partly reshaped cornea.

[0059] Turning now to FIG. 7, an edge portion of the peripheral zone 26is shown schematically, and is specially designed to provide comfort andproper function in a contact lens for normal wear or in CRT process. Asshown in FIG. 7, the edge of a lens according to the invention may beprovided with a smoothly contoured profile, which is facilitated by thegenerally parallel relationship between the interior and posteriorsurfaces in the peripheral zone 26, as well as by the straightness ofthe peripheral zone 26 itself in this embodiment. The edge terminus ofthe peripheral zone 26 is shown in cross-section in FIG. 7, and adividing line bisecting the lens at this region may be envisioned. Sucha dividing line may be envisioned to be substantially parallel to andbetween the anterior and posterior surfaces as shown at 150. Thisimaginary dividing line may be nearer to the anterior or posteriorsurface in the edge region. In the embodiment as shown in FIG. 7, thisline may be positioned in closer relationship to the posterior surface.A designer can then imagine a quadrant of an ellipse whose center is onthis dividing line and whose long axis would extend from the selectedellipse center along the chosen dividing line, to just reach the veryedge of the lens. The short axis of the ellipse would extendperpendicularly to the long axis from the center point to contact one orthe other sides of the lens. As shown in FIG. 7, the short axis extendstoward the posterior surface meridional profile to intersect theposterior profile. Where the short axis reaches the edge, the ellipsewould parallel the edge, and where the long axis reached the tip, theellipse would have curved so as to be perpendicular to the edge at thepoint where it meets the dividing line. The profile of the quadrant ofthe ellipse thus merges smoothly with the profile of the peripheral zone26 and replaces that portion of the meridional profile of the peripheralzone 26 in that region beyond the intersection of the short axis and theprofile of the peripheral zone 26 to become the profile of the posteriorlens terminus. This posterior terminus can join a similar but invertedstructure on the profile of the anterior surface of the lens at theultimate tip of the lens to form a smooth junction. The dividing linebeing chosen to be at a location 10 to 90% of the thickness of the lensfrom the posterior to the anterior and the long axis of the ellipsechosen to be about 0.01 mm to 2.0 mm in length.

[0060] A “mirror image” of this ellipse may be imagined on the otherside, joining the anterior cross-sectional edge to the tip. The apicesof the ellipses would necessarily meet at the dividing line 150, at thetip, and each would roll back to parallel an adjacent edge of the lens.When the dividing line is not midway between the anterior and posteriorsurfaces, the ellipse quadrants would be differently shaped, but wouldalways smoothly join each other at the tip, and roll smoothly back tomeet the original cross-sectional edges. The two ellipse quadrants neednot have equal long axis, although their short axis are defined by theplacement of the original dividing line 150. By manipulating thelocation of the dividing line between the anterior and posteriorsurface, such as by a fraction of this thickness, and manipulating thelengths of the long axis of the ellipse quadrants in each ellipse, onecan achieve mathematically and geometrically a desired edge shape. Adesired edge shape is then easily cut by means of computer controlledlathes or the like. Altered edge configurations may be better suited toa particular patient, to better accommodate patient characteristics,such as lid aperture and tightness, as well as high amounts ofperipheral astigmatism in the corneal shape. The ability to alter theedge configuration again makes the lens according to the inventionflexible and adaptable to a particular patients needs, while providing asimple design which is more easily fitted to the particular patient. Inexamples as will follow, in many cases, the edge configuration suitablemay include using equal long axis of 0.4 mm, with a dividing line 150 atapproximately 25% of the way between the posterior and anterior surfacesof the lens. Another example as will be seen hereafter, provides analtered edge configuration for use with a very large diameter lens,which includes a thick peripheral zone, for use on corneas with higheccentricities. In such a special case, a long axis of 2 mm with adividing line at 45% of the distance between the posterior and anteriorsurfaces may be desirable. It should also be recognized that theanterior profile of the peripheral zone can be designed to have anequivalent angle to that of the posterior profile in the peripheralzone. The anterior lens terminus will have an elliptical curvaturederived from a quadrant of an ellipse and extending to the intersectionpoint with the posterior surface.

[0061] Turning now to FIGS. 8A-8C, in the design of the peripheral zone26, the angle of the conoid and its chord diameter D₃ are preferablychosen so that upon engagement with the cornea after redistribution ofcorneal tissue as described above, the first point of contact of thecornea with the peripheral zone 26 is approximately midway between thejunction (J₂) of the peripheral zone 26 with the connecting zone 14 andthe outside peripheral edge of the lens 10, and may be slightly nearerthe peripheral edge. This engagement is shown in FIG. 8A for a portionof zone 26 on cornea 30. In this manner, the chance of “toe down” or“heel down” engagement of the peripheral zone 26 with the cornealsurface, as shown in FIGS. 8B and 8C respectively, is minimized. Suchheel down or toe down engagement can lead to corneal abrasion or othercomplications, and in general, creates undesired discomfort andminimizes the extent of achievable correction. These conditions areeasily avoided even after treatment completion when the non curving(infinite radius) peripheral zone is employed, but which are common(probably mandatory) with common ortho K lens designs which use corneafacing concave curvatures with radii less than 17 mm. It remainsunrecognized by those skilled in the art that much flatter radii aredesirable, as historically making such curves with lathes designed tocut radial arcs has been very difficult.

[0062] As described above, the peripheral zone 26 is designed to beelevated from the cornea at initial stages of treatment, with firstengagement of the cornea with zone 26 occurring after a predeterminedamount of corneal tissue redistribution. After first engagement, furtherredistribution of the central cornea will lead to further engagement bythe flat peripheral zone 26. Further engagement with the peripheral zonewill result in symmetric spreading in the width of the engagement zoneabout the point of first engagement, which ultimately will deteradditional corneal flattening while still avoiding heel down or toe downengagement.

[0063] In general for a CRT procedure, a designer may start with adiameter approximately 1 mm smaller than the (HVID). The HVID gives agood estimate of the total size of the cornea. The designer then canfind the angle whose point of tangency is half way to two thirds of theway from J2 at 8 mm (the sum of standard central zone width (6 mm andconnector zone width 1 mm (2 mm considering both sides)) and the overalldiameter. The lens base curve is computed from central keratometry andthe correction required so all that is left is to use one method oranother to determine the rectangle depth that leaves the tangent pointelevated above the cornea approximately 3-7 microns per diopter ofneeded correction. The angle of the truncated conoid forming theperipheral zone 26 in the embodiment as shown is determined to assurethat the ultimate engagement of the peripheral zone 26 will besufficiently far from the junction J₂ with connecting zone 14 to avoidtoe down engagement. This determination may be made by simultaneousmodeling of the patients cornea and a lens designed in accordance withthe present invention to visually or mathematically determine the pointof engagement upon corneal tissue redistribution, or the same point maybe located by trial fitting. With the angle of the conoid determined, itis possible then to select the final diameter of the lens, which ingeneral is selected in trial fitting by noting the diameter at which aflat surface will deviate from the corneal surface sufficiently to yieldthe lens designer or fitters desired “edge lift”. The edge lift of theperipheral zone 26 is the region at the periphery of the lens which isgenerally required to assure good tear flow under the lens, and to moreclosely approximate the corneal shape when excursions are made beyondthe limbus. This will avoid abrasive interaction between the peripheryof rigid lens and the corneal and scleral surface. This edge lift iscommon to all rigid lens designs as is well known to those skilled inthe art of rigid lens design and fitting and is described in textsrelating to rigid lens fitting. Beginning at the tangential contactpoint of the peripheral zone 26 with the redistributed corneal tissue,and extending the peripheral zone 26 outward, the posterior lens surfacedeviates further and further from the cornea generally. In the lensdesign, the diameter will normally be set at a value where thisdeviation between lens and cornea is estimated to be sufficiently greatto allow required tear flow under the lens. It should be recognized thatthe simplicity of selecting a proper diameter for the lens 10 accordingto the invention for a given lens or patient provides a significantadvantage to the lens designer. In an embodiment, the posterior surfaceof the truncated conoid effectively provides a flat surface relative tothe curved surface of the cornea, the proper diameter to achieve thecontact between the peripheral zone 26 and cornea as described above isrelatively simple, as compared to use of a curved arc. With a curvedarc, estimating the location of the first engagement with this arc andthe curved cornea is more difficult, and even further, estimating theedge lift at a given diameter is also difficult to accomplishaccurately. Thus, providing the peripheral zone 26 in accordance withthis embodiment of the invention simplifies the design process, andmakes proper fitting of the lens easier and more cost effective.

[0064] The design of the peripheral zone 26 is also beneficial to thelens designer in other respects. In some patients, the lens design maybe susceptible to decentering, and the fitter will look to stabilize adecentering lens using a larger diameter. Using a peripheral zone 26which is non-curved, the angle of the conoid of the peripheral zone 26may simply be increased to move the contact point of peripheral zone 26with the cornea further from the junction with connecting zone 14allowing a larger diameter to be used without excessive edge lift.Again, because the zones of the inventive lens are separate and distinctfrom one another, the ability to increase the angle of the peripheralzone 26 is provided without effecting the design elements of the centralzone. Again this process is easily visualized by a lens designer orfitter to arrive at an acceptable design more easily than in prior artlens configurations. Designing the peripheral zone 26 in accordance withthe principals of the invention provides a lens design which eitherinitially or in some cases a final lens of a treatment series, providesa lens which may be continuously used by a patient as a “retainer” lens.For such a purpose, the “retainer” lens must in its final engagementconfiguration perform as a typical rigid contact lens would, with regardto tear flow, centration and non-abrasive contact. Providing theperipheral zone to tangentially engage the curved cornea in the finalengagement configuration assures this relationship after redistributionof the corneal tissue is completed. This eliminates the need for anadditional lens dispensing after correction has been achieved.

[0065] Several examples are set forth below.

EXAMPLE 1

[0066] This example is based upon a patient having a prescription asfollows:

[0067] 1. 44.50×46.00@180, Rx −4.00−0.75×180, e=0.5, HVID 11.6

[0068] Based upon the prescription of patient 1 above, a lens designerwould select the power of the lens to correct the patient to a desireddegree. In this example, with reference to FIG. 9, the lens/cornea powerdifference wanted for patient 1 is selected as −4.5 diopters asindicated at 200. The power difference selected is slightly more thanthe degree of correction required for the patient, to allow substantialcorrection of visual acuity over a longer period of time after reshapingof the cornea using the lens according to the invention. Patient 1 alsohas a fairly high astigmatism of 0.75, and the ellipticity of the corneais 0.5 as shown at 202. Patient 1 has an HVID of 11.6, as noted at 204,and based upon this HVID, the diameter of the lens which is recommendedis 10.6 mm as indicated at 206, being 1 mm less than the measured HVID.The selected diameter for the lens is shown at 209, being chosen basedupon the recommended diameter and the relationship between the zones ofthe lens. Based upon the lens/cornea power difference wanted, a basecurve of 8.4 is selected for this patient as indicated at 208. Otherparameters of the lens may be selected which provide desiredcharacteristics for most patient conditions, including the radialdistance from the lens center to the junction between the base curve andthe sigmoidal curve, indicated at 210 as 3.0 in this example. The widthof the sigmoidal curve is selected to be 1.0 mm as indicated at 212, thelens power is selected at 214, representing examples of variables whichcould be used to modify characteristics of the lens, but to simplifylens design, may be held constant to limit the number of variables usedby the lens designer. Based upon the desired correction, it waspreviously mentioned that the peripheral zone is initially elevatedabove the cornea to a predetermined degree to provide for redistributionof corneal tissue to a predetermined shape. The angle of the peripheralzone 216 is selected to be −35 to provide the proper relationship to thecornea as to spacing and to avoid toe down or heel down engagement aspreviously described. As an example, the elevation of the peripheralzone above the cornea can be selected at six microns per diopter ofcorrection to be imparted by the base curve. As indicated at 218, therecommended depth of the sigmoidal curve for providing the desiredelevation of the peripheral zone is 0.51 mm. Based upon these factors,the lens designer can note the relationship of the surface visually,such as shown in FIG. 10, representing the elevation of the posteriorsurface from the cornea along a semi-chord diameter of the lens. Asseen, the base curve 250, the sigmoidal curve 252 and the peripheralzone 254 are shown in relationship to one another, and allow thedesigner to select the proper diameter of the lens. To achieve propertangential contact between the peripheral zone and the cornea uponredistribution of corneal tissue as previously described, the positionof the peripheral zone can be determined, along with its angle, allowingthe fitter to vary the depth of the sigmoidal curve to obtain the properrelationship to the cornea. Variations of the depth of the sigmoidalcurve will in general move the peripheral zone curve 254 up and down inthe graph of FIG. 10, while changing the angle of the peripheral zonewill move this surface right or left. It should be evident that therelationship of the surfaces relative to each other and to the corneaare easily visualized and facilitate simple and proper design of thelens for a particular patient. It is also possible to show theindividual and cumulative volumes under the lens according to aparticular design of this type, such as shown in FIG. 11, relative to amodel cornea. This representation of the lens design provides thedesigner with an easy tool for identifying any void spaces, which maylead to the creation of bubbles beneath the lens. A semi-meridiansection 255 of the lens according to this example is shown in FIG. 12,and the front and back individual curves for each of the zones 12, 14and 26 are shown in FIG. 13. It is noted that the thickness of thecentral and peripheral zones remain substantially constant, with thesigmoidal curve thickness transitioning between the two, as shown inFIG. 13. Due to the relatively high astigmatism of patient 1, thethickness of the peripheral zone is increased slightly relative to thecentral zone to avoid possible warping of the lens over time by lidpressure applied thereto. It is possible to change the thicknesses ofthe zones simply, allowing great flexibility in designing the centraland peripheral zones in a desired manner to achieve proper lensstability as well as to allow proper oxygen transmission and tear flowbeneath the lens. With reference to FIG. 9, to change the centerthickness, a designer may vary the delta r value for the junctionbetween the base curve and the sigmoidal curve as shown at 222. Thiscontrols the thickness of the lens at that location, and allowscalculation of the true center thickness at 224 based upon the power ofthe lens. Again, it is possible to limit the variables to simplify thedesign of a lens which would cover most patient conditions, butflexibility exists in the lens design and system according to theinvention, to facilitate achieving the desired objectives for a givenpatient.

EXAMPLE 2

[0069] For patient 2, having a prescription as follows:

[0070] 42.00×44.00@165, Rx −3.50−1.00×160, e=0.6, HVID 11.4

[0071] With patient 2, a relatively high refractive error along withhigh astigmatism is noted, which again will lead the lens designer toincrease the value of the ellipticity of the cornea as shown at 230 inFIG. 14. Due to the high astigmatism, it is desired to have a thickercenter in the lens, which again is easily accommodated by varying thedelta r for the first junction between the base curve and the sigmoidalcurve as shown at 232. Other aspects of the particular lens design forpatient 2 are determined in a manner similar to that described withreference to patient 1 in Example 1. Particular values for thevariables, including base curve, lens diameter, angle of the peripheralzone as well as depth of the sigmoidal curve are shown in FIG. 14, withthe relationship between the zones shown graphically in FIG. 15. Therelatively thick center and thinner edge portion in this lens design isvisually represented in the semi-meridian section 255 in FIG. 17, withindividual and cumulative volumes under the lens shown in FIG. 16. FIG.18 shows the relationship of the front and back surfaces in each zone12, 14 and 26 relative to one another.

EXAMPLE 3

[0072] For patient 3 having a prescription as follows:

[0073] 46.50×46.50@180, Rx −6.00−0.75×90, e=0.4, HVID 11.2

[0074] With reference to FIGS. 19-23, a lens design according to thepresent invention for patient 3 is shown. Selecting parameters of thebase curve, base diameter, angle of peripheral zone as well as depth ofthe sigmoidal curve are selected in a manner similar to that previouslydescribed, providing a first indication of fit to the lens designer. Forpatient 3 using a value of 3.0 mm as the radial distance from the lenscenter to the first junction, which may in general be held uniform,produced a relatively large void space adjacent the base curve at thefirst junction. The lens designer therefore has the flexibility toreduce or narrow the optical zone, as indicated by the use of 2.5 mm at210 and increases the width of the sigmoidal curve indicated at 212 as2.0. The relationship of the zones relative to one another and thecornea are shown in FIGS. 20-23, wherein the void space adjacent thebase curve at junction 1 was reduced.

EXAMPLE 4

[0075] For patient 4 having a prescription as follows:

[0076] 41.50×43.00@180, Rx −5.00−0.75×180, e=0.3, HVID 11.9

[0077] Patient 4 has a large refractive error, as well as a large HVID,translating to a relatively larger lens diameter than previous examplesas shown at 209. At the same time, patient 4 has a low ellipticity, suchthat proper support for the lens may not be provided at peripheralregions. In this circumstance, it is possible that lens might warp orbend out on the outside peripheral edges due to the low ellipticity,such that the designer may wish to thicken the outside portion of thelens. At the same time, thickening the peripheral regions of the lenswill reduce oxygen transmission to the cornea, and therefore thedesigner may wish to reduce the thickness of the central zone to allowbetter oxygen transmission. As shown in FIGS. 24-28, a lens designedaccording to the invention for patient 4 may accommodate such changes byreducing the delta r translation of the first junction at 222 andincreasing the delta r translation of the second junction at 242.Although these modifications allow redistribution of mass toward theperipheral region of the lens as shown in FIG. 27, and reduces thethickness of the central zone, the lens designer may also want to extendthe edge profile and control the edge shape to minimize discomfort. Inthis example, the edge contour provided in a desired design is startedearlier to reduce the mass at the very peripheral regions of the lens asshown in FIG. 29 reducing the mass at the edge where the eyelid willengage the lens facilitates comfort. To facilitate shaping the edge inthis manner, the parameters of the ellipse creating the posterior curveedge are modified at 243, 244 and 245 to facilitate imparting thedesired edge contour and promoting tear flow and oxygen transmission.

EXAMPLE 5

[0078] For a patient 5 having a prescription as follows:

[0079] 43.50×44.00@180, Rx −3.00, e=0.7, HVID 11.0

[0080] For patient 5, it is noted the cornea is very spherical with noastigmatism. In such a case, lens stability concerns are minimized, andthe lens may be made thin at central and peripheral portions. Reducingthe thickness of the lens may be accomplished by reducing the delta rtranslation points for the first and second junctions as shown at 222and 242 in FIG. 30. FIGS. 31-34 show the lens design for patient 5 inmore detail.

[0081] In the above examples, the prescriptions represent a very widerange of myopic corneas. It should also be recognized that the lensdesign can accommodate patients having hyperopia. In such a lens, thefinal desired shape of the cornea is achieved by redistributing cornealtissue to form a steeper corneal surface. Thus, such a design wouldtypically use a steeper base curve accordingly, which in turn wouldsuggest a greater apical separation between the cornea and lens toensure the base curve does not penetrate the cornea when analyzed on amodel cornea. The central zone may also be narrower, which again iseasily accomplished by widening the connecting zone in the lens design.The peripheral zone may also need not be elevated from the cornea atinitial stages to the degree a myopic design would, due to thecorrection to be imparted to the corneal shape, as the lens willeffectively be squeezing the cornea from a larger annular zone to fill asmaller central zone of the lens.

EXAMPLE 6

[0082] For a patient 6 having a hyperopic prescription, the lens wasdesigned as follows: The lens design for the hyperopic condition ofpatient 6 is shown in FIGS. 35-39. The lens is designed to provide alens/cornea power difference for patient 6 of 2.0 diopters as indicatedat 200 in FIG. 35. The selected base curve has a 7.50 mm radius, asindicated at 208. The power difference may again be selected as slightlymore than the degree of correction required for the patient, if desired.Other parameters of the lens may be chosen similarly to that previouslydescribed, such as lens diameter. The lens is then designed to have anarrower central zone, with the radial distance from the lens center tothe junction between the base curve and the sigmoidal curve, indicatedat 210, being reduced to 2.5 mm in this example. In turn, the width ofthe sigmoidal curve at 212 is increased to 1.5 mm. The height above thepretouch peripheral zone and cornea is somewhat less in this example,indicated as 0.024 mm at 244. Similarly, the volume between the pretouchperipheral zone and cornea is less in this example, indicated as 0.491(uL) at 246, and as shown in FIG. 37. The apical separation of the lensfrom the cornea is chosen to ensure the base curve doesn't penetrate thecornea, as indicated in the graph of FIG. 36 at 250.

[0083] As previously mentioned, it may be desirable in practice to limitthe number of variables which are modifiable to design the lens forsimplifying the design process. As an example, lenses can be designedlimiting the variables to BC, DIA, sigmoidal curve depth and peripheralzone angle. The patients and lenses in the examples include relativeextremes, one could imagine unusual problems that might occasionallyarise with such patients. In the examples, additional parameters werethen modified as needed to alleviate any problems in properly fittingthe unusual patient. All patients were successfully fit as the graphsand measures show. Other variables beyond the BC, DIA, sigmoid curvedepth and peripheral zone angle can then be used to treat these specialcases. Additional variables include but are not limited to: Thickcenter/thin edge, such as shown in Example 2, which has very highcylinder and eccentricity warpage was possible. For Patient 3 which hada very high correction, requiring a big discrepancy between cornealradius and base curve, this led to a large volume at junction 1 so inthis case the central zone diameter was reduced and the connector zonewidened with the expected result bringing the connector closer to thecornea and reducing bubble possibilities. The low eccentricity exhibitedby patient 3 has led to high edge lift and junction 2 elevation. Asmaller diameter and lower angle would solve this problem if the patientfound the lens uncomfortable.

[0084] Patient 4 was prescribed a very large diameter lens, allowed bytheir large HVID to assure good centration on his high correction andcylinder This will reduce oxygen under the lens from tear movement, anda thin center was provided. Extra thickness on the outside was added tominimize warpage but to make this thick edge comfortable the edge zonewas extended to 2 mm and the dividing line moved away from the basecurve for extra tear pumping.

[0085] Patient 5 is very spherical with high eccentricity, such that thelens will hug the cornea, thickness could lead to excessive movement sothis patient offers an opportunity for extra oxygen and comfort with thethin profile throughout. As seen in FIG. 18 as an example, showing therelationship between front and back surfaces, the anterior surface isdesigned to substantially mirror the posterior surface zone 12 andperipheral zone 26, while the connecting zone 14 is designed such thatthe posterior and anterior curves deviate from one another to apredetermined degree. As mentioned previously, the front or anteriorsurface may be designed such that there is different spacing between thesurfaces from the apical point to the peripheral edge of the lens, forexample to provide better oxygen transmission to the center of the lensand yet provide desired structural support at the periphery of the lens.The spacing difference is easily adjusted by adjusting the length andwidth of the anterior sigmoidal curve as compared to the posteriorsigmoidal curve. As shown in FIG. 17, a semi-meridian section of analternative embodiment is shown to include varying thickness toward theperiphery of the lens.

[0086] In accordance with the lens design as described according to thepresent invention, it is then possible to provide a method of fitting apatient with an CRT for treatment, such as shown in FIG. 40. Thepatient's visual acuity and corneal curvature is measured at 350 todetermine the present shape of the cornea and enable a practitioner toselect a base curve for correction of the corneal shape to a desireddegree. The determination of the base curve of the central zone toaffect desired corneal reshaping at 352 is then made, providing thedesign of the central zone 12. Thereafter, at 354, the diameter of thelens is determined, such as by measurement of the HVID. The slope of theperipheral zone may then be selected at 356, to in effect provide thedesign of the central zone 12 and peripheral zone 26 relative to a givenpatients cornea and the desired correction to be imparted. With thisinformation, the sigmoidal curve of the connecting zone 14 is designedat 358 for connecting the base curve 12 and peripheral zone 26. Theproper rectangle depth for the sigmoidal curve which leaves the tangentpoint elevated to a predetermined height above the cornea can bedetermined at 358, with the fitter able to compare the lens design to amodel eye, by fluoroscene with trial lenses, or topographicalinformation. If necessary, the relationship of the lens zones to thecornea can be adjusted by varying the connector zone depths. The lensdesign can then be compared to a model eye using software, and triallenses can be fit on the patient to verify the lens design, andparticularly the design of each of the independent zones 12, 14 or 26 asshown at 360.

[0087] As previously mentioned, the method of fitting as described mayaccount for a series of lenses, designed to progressively impart partialcorrection to the corneal shape until the final desired correction isachieved. In the method of fitting, adjustment of the lens design,visualization and assessment of the lens design, and the ability toteach and communicate design variables to a fitter are facilitated andenabled by the lens design itself. The method of fitting could utilizeadjustments in the sagittal depth of the lens 10 to adjust the cornealreshaping characteristics of the lens by changing the axial length ofthe connecting zone 14. Adjustments of the axial length of theconnecting zone 14 result in directly corresponding changes in thesagittal depth of the lens 10. Similarly, the method of fitting mayinclude varying the volume distribution of the void space createdadjacent the base curve 12 in association with the connecting zone 14.As previously mentioned in a CRT and/or Ortho K treatment process, thecharacteristics of this void space enable corneal tissue to beredistributed in the desired manner. Changes to the volume of this spacemay be provided by varying the diameter of the central zone 12, theaxial length of the connecting zone and the radial width of theconnecting zone, without otherwise affecting the lens design and fit.The method of fitting also allows changes to the radial location ofpossible tangential contact of the redistributed cornea to theperipheral zone 26 by varying the angle of the peripheral zone 26 to thecentral axis of the lens, again without otherwise affecting the lensdesign and fit. The edge contour which may be desired in the peripheralzone 26 is also easily adjusted by changing the extension of the lensbeyond the point of possible tangential contact of the peripheral zonewith the cornea of the wearer. The edge profile itself is also easilymodified by changing the axes of imaginary ellipses, and the location ofthe imaginary dividing line between the posterior and anterior ellipses.

[0088] The method of fitting can thus allow the manufacture of a lensset having the central zone diameter, connecting zone width, lensdiameter and edge profile provided with predetermined shapes. With sucha lens set, the fitter then measures the preferred corneal curvatureneeded to eliminate refractive error for a patient, and may measure thecentral corneal curvature of the patient's cornea. Thereafter, thefitter need only determine two parameters, the connecting zone depth andperipheral zone angle from fitting or computer modeling. As previouslydescribed, the parameters of connecting zone depth and peripheral zoneangle may be derived by fitting lenses from a fitting set having a fixedconnecting zone depth with a series of base curves or a fixed base curvewith a series of connecting zone depths and another set having a fixedconnecting zone depth with a series of peripheral zone angles from whichthe final selection is derived. Again, it is also possible to providethe set of fitting lenses with a plurality of visible concentric ringsas mentioned with respect to FIG. 4, to determine the lens diameter atwhich substantially tangential touch occurs between the lens and thecornea, and thereby determine the angle of the at least one peripheralzone.

[0089] As stated previously, the fitting of the lenses is simplified asthe fitter is able to easily visualize the fit of the lens inassociation with a patient' cornea. In FIG. 41, a schematicrepresentation of the patients eye and cornea are shown with the lensdesign positioned thereon. The actual corneal surface is represented bythe ellipse at 452. In assessing the fit of the lens 450 on the cornea452, particularly at the peripheral regions where the peripheral zone ofthe lens is positioned, the cornea can be approximated by a circle 454over a portion of the corneal surface. As can be seen, the circle 454 istangent to the ellipse 452 at the peripheral portion of the cornea. Todetermine the appropriate fit of the lens 450, the characteristics ofthe lens can be determined and changes in parameters visualized. Frommeasurement or observation, the fitter provides information regarding atest lens 450 positioned on the patient's cornea, particularly the angle(A1) used in the lens of the test series. As seen in FIG. 41, the lens450 tangentially touches the cornea represented by the circle 454 at 456relating to the touch diameter 1 (TD1). The optimum location, or touchdiameter 2 (TD2), for the tangential touch of the peripheral zone as setforth previously is then determined, and shown at 458, yielding a changein the height and width of triangles formed between the center of circle454, the touch diameters TD1 and TD2 and the line perpendicular to avertical radius of the sphere 454. With these parameters identified, thechange in the height and width result in a change in the connecting zonedepth (RZD). The radius of the sphere 454 to be determined relating tothe spherical cornea which would have a tangential contact with a lineat angle A1 from a line perpendicular to a vertical radius of the sphereby Eq. 9: $\begin{matrix}{R = \frac{{TD}\quad {1/2}}{{SIN}\left( {A\quad 1} \right)}} & \left( {{Eq}.\quad 9} \right)\end{matrix}$

[0090] where H is the distance along the vertical radius of the spherefrom the origin to the intersection with the sag diameter passingthrough the tangential point when A1 is fitted by Eq. 10.$\begin{matrix}{{H\quad 1} = \frac{{TD}\quad {1/2}}{{TAN}\left( {A\quad 1} \right)}} & \left( {{Eq}.\quad 10} \right)\end{matrix}$

[0091] Using R from above, we can calculate TD2 and H2 by Eqs. 11 and12:

TD2=2*R*SIN(A2)  (Eq. 11)

H2=R*COS(A2)  (Eq. 12)

[0092] The difference between the height for A1 and A2 is found bysubtraction, as is the difference in sagittal diameter. Both of thesevalues are arranged to yield positive values when A2>A1 by Eqs. 13 and14.

ΔH=H1−H2  (Eq. 13)

ΔW=2*(TD2/2−TD1/2)   (Eq.14)

[0093] Considering the smaller triangles in the upper right of FIG. 41,where x and y are the horizontal and vertical components respectively,these coordinates are found as follows:

x1=TD1/2−J2   (Eq.15

y1=x1*TAN(A2)  (Eq. 16)

x2=Td2/2−J2   (Eq. 17)

y2=x2*TAN(A2)  (Eq. 18)

[0094] From this, the change in the connecting zone depth RZD isdetermined

ΔRZD=y1−y2  (Eq. 19)

[0095] with the relationship between peripheral zone angle andconnecting zone depth seen to correspond in a manner the fitter canvisualize and verify proper fit of the lens. In the example shown inFIG. 41, the RZD change is only the component due to an angle change,and base curve changes must be independently considered. In thisexample, the original parameters observed relating to the fit of thefitting lens and the resultant changed parameters are given as follows:J2 radius 4 Angle A1 −32 RZD change due to angle change only Angle A2−33 −0.023 Touch Diameter 9.75 10.02083 touch diameter after change

[0096] The present invention also provides for a method of establishingcentration over the visual axis of the lens by adjusting the location ofpossible peripheral tangential contact and the extension of the lensbeyond the point of peripheral contact of the lens with the cornea.

[0097] This ability in the lens design would allow better fitting of anycontact lens, not just for corneal refractive therapy, and would enhancecomfort and provide other advantages by maintaining centration of thevisual axis over the cornea.

[0098] The present invention is also directed at a computer programproduct for designing orthokeratology contact lenses. A person ofordinary skill in the art would appreciate that the invention may beembodied as a method, data processing system, or computer programproduct. As such, the present invention may take the form of anembodiment comprised entirely of hardware, an embodiment comprisedentirely of software, or an embodiment combining software and hardwareaspects. In addition, the present invention may take the form of acomputer program product on a computer-readable storage medium havingcomputer-readable program code embodied in the medium. Any suitablecomputer-readable medium may be utilized including hard disks, flashmemory cards, CD-ROMs, optical storage devices, magnetic storage devicesor the like.

[0099] The method of fitting and the computer program product of theinvention are described with reference to flow charts or diagrams thatillustrate methods, and systems, and the computer program product. Itshould be understood that each block of the various flow charts, andcombination of blocks in the flow charts, can be implemented by computerprogram instructions. Such computer program instructions can be loadedonto a general-purpose computer, special purpose computer, or otherprogrammable data processing device to produce a machine, such that theinstructions that it executes on the computer or other programmable dataprocessing apparatus, create means for implementing the functionsspecified in the flow charts. The computer program instructions can alsobe stored in a computer-readable memory that directs a computer or otherprogrammable data processing device to function in a particular manner,such that the instructions stored in the computer-readable memoryproduce an article of manufacture including instruction means whichimplement the functions specified in the flow charts or diagrams. Thecomputer program instructions may also be loaded onto a computer orother data processing apparatus to cause a series of operational stepsto be performed on the computer, to produce a computer implementedprocess, such that the instructions which execute on the computer orother programmable apparatus provide steps for implementing thefunctions specified in the flow charts or diagrams.

[0100] It will also be understood that blocks of the flow charts supportcombinations of means for performing the specified functions,combinations of steps for performing the specified functions and programinstructions means for performing the specified functions. It is also tobe understood that each block of the flow charts or diagrams, andcombination of blocks in the flow charts or diagrams, can be implementedby special purpose hardware-base computer systems which perform thespecified functions or steps, or combinations of special purposehardware and computer instructions.

[0101] The software program of the present invention could be written ina number of computer languages, and any suitable programming language iscontemplated. It is also to be understood that various computers and/orprocessors may be used to carry out the present invention, includingpersonal computers, main frame computers and mini-computers.

[0102] In FIG. 42, the user first inputs the corneal apical radius andellipticity, as well as the suggested base curve for correction ofvisual defects of a patient at 400. It is then determined whether a basecurve is available for total correction of the visual defects of thepatient at 402. If not, the user selects a base curve for partialcorrection at 404, or if such a base curve is available, the user inputsthe base curve and the diameter of the selected curve at 406. The userthen inputs the parameters of the diameter at 408, and selects theparameters of the peripheral zone angle at 410. The parameters of thesigmoidal curve are input at 412 as well as the lens power at 414. Theparameters of the edge design may be input at 416. The lens is designedusing the input parameters, and the relationship of the designed lens toa model cornea is determined at 418. From this analysis, it isdetermined whether the lens design is acceptable at 420, and if not thesystem returns to selection of a base curve at 402 or redesign of theother zones for redesign of the lens.

[0103] In an embodiment of the invention, a hand-held computer, such asa Personal Digital Assistant (PDA), is programmed with the computerprogram of the invention, to compute the best lens fit from the fittersobservations. The program may utilize different approaches as previouslydescribed, such as the angle series of fitting lenses wherein thefitting lens set has a fixed base curve with a series of connecting zonedepths and another set having a fixed connecting zone depth with aseries of peripheral zone angles from which the final selection isderived. Another approach as described may utilize the fitting lenseshaving concentric visible rings to determine the diameter of the desiredtangential touch and compute the angle of the peripheral zone. In bothmethods, the computer program will prompt the user for inputs relatingto a flat keratometry reading on the patient, the patients refractiveerror, the final target refractive error (usually piano but may bedifferent), the horizontal visible iris diameter and the lens code forthe fitting set lens that just touched centrally and peripherally. Theprogram will prompt the user for the angle of the lens from the angleseries of fitting lenses whose tangential touch was at the preferredlocation as described. The other method requests the diameter at whichfitting set lenses (all having the same angle) displayed their ring oftangential touch.

[0104] Upon determining an acceptable design, lathe parameters andcutting data is calculated and generated at 422. As previouslymentioned, based upon the lens characteristics according to theinvention, it is possible to provide “unfinished base curve buttons” tobe inventoried by lens finishing labs or other similar entities. Usingthe unfinished base curve button, a lens finishing lab may be given thelathe parameters and cutting data for a particular lens, which aresimply downloaded to a computer controlled lathe for generating theparticular lens design for a patient. In the unfinished base curvebutton, the buttons may be provided with a portion of the finished edgeat a fixed diameter or may be provided with the maximum diameter to becommercially provided. In the latter case, when the fitter specifies therequired diameter, the lenses can be cut down to that diameter in thearea of the peripheral zone without any effect upon the rest of theprecut portions of the lens. Thus, one button having particular basecurve and sigmoidal curve characteristics may be used for all possibleperipheral zone diameters. Further since all aspects of lens opticalpower are provided on the anterior surface of a finished lens, a basecurve selected to fit a particular patient may be employed to make alens of nearly any optical power. This inventory advantage exists evenif the button is already provided with a predetermined diameter and edgecontour. In this way, the number of buttons to be inventoried isminimized, while providing significant flexibility in the ultimate lensdesign. The ability to provide lathe cutting instructions to thefinishing lab also greatly simplifies manufacture of a lens according tothe invention, again greatly facilitating use of such lenses as well asreducing costs thereof and assuring reproducibility regardless of thelab of origin.

[0105] The present invention may also accommodate multifocals andastigamatic lenses, both of which use the design according to theinvention, but toric lenses for astigmatism and/or improved peripheralfit (on non-spherical eyes). With the design approach, this allows thedesigner to choose two orthogonal meridians of corneal shape, anddesigning a corresponding portion in the lens for each separately.Present lathe technology can accept designs that vary in two meridians,and the design of the invention makes programming these lathes as easyas non-toroidal designs. One simply subtracts the z axis value of onemeridian at each x point and uses this data as difference data to beused by the lathe during each rotation. The technique is not limited totwo orthogonal meridians, but could incorporate many such meridians.

[0106] One of the benefits of the present invention is the ability toprecisely control the elevation of the lens center with respect to thecorneal surface. In CRT, the center of the lens may contact the centralcornea, but some situations exist where one wishes to minimize oreliminate this contact. In normal rigid lenses, this control is obviatedby the use of base curves that mimic the corneal surface, and thus nochange arises as a result of the contact. But in some situations, it isdesirable to have a different geometry on the base curve. Presbyopiclenses with multiple curves are a case in point, though other situationsalso exist. Being able to support a lens off of the corneal surface canmake many new base curve geometry designs possible, as multifocals arean example. It is also possible to provide the base curve with ageometry which when that geometry is impressed on the cornea could makeit multifocal. Such base curves may thus be formed with one or morespherical or aspherical zones to provide these characteristics. Thebenefits are obvious, such as allowing a patient to wear contact lenseswhile they sleep to avoid wearing reading glasses during the day.Examples of other applications for the present invention could alsoinclude providing a corneal shape controlling device to control orimprove laser surgery. Use of the invention could reduce failures andannoying compromises.

[0107] The foregoing disclosure is illustrative of the present inventionand is not to be construed as limiting the invention. Although one ormore embodiments of the invention have been described, persons ofordinary skill in the art will readily appreciate that numerousmodifications could be made without departing from the scope and spiritof the disclosed invention. As such, it should be understood that allsuch modifications are intended to be included within the scope of thisinvention. The written description and drawings illustrate the presentinvention, and are not to be construed as limited to the specificembodiments disclosed.

What is claimed is:
 1. A corneal contact lens comprising a central zonehaving a posterior surface curvature, a connecting zone having aposterior surface and provided adjacent and concentric to said centralzone, said connecting zone having a shape defined as a sigmoidal curve,and at least one peripheral zone having a posterior surface and providedadjacent and concentric to said connecting zone.
 2. A corneal contactlens according to claim 1 wherein the curvature of the central zone isspherical.
 3. A corneal contact lens according to claim 1 wherein thecurvature of the central zone is toric.
 4. A corneal contact lensaccording to claim 1 wherein the curvature of the central zone isaspherical.
 5. A corneal contact lens according to claim 4 wherein thecurvature of the central zone comprises a combination of annularspherical and aspherical zones.
 6. A corneal contact lens according toclaim 5 wherein the curvature of the central zone comprises acombination of spherical and aspherical zones.
 7. A corneal contact lensaccording to claim 1 wherein the central zone is designed to correctpresbyopia without contacting the cornea.
 8. A corneal contact lensaccording to claim 1 wherein the central zone is designed to correctpresbyopia by reshaping the cornea.
 9. A corneal contact lens accordingto claim 1 wherein the meridional profile of the connecting zone isshaped to match the slopes of the central zone and the at least oneperipheral zone on adjacent sides.
 10. A corneal contact lens accordingto claim 1 wherein the meridional profile of the connecting zone isdescribed by its axial length and horizontal width.
 11. A cornealcontact lens according to claim 1 wherein the junctions between theconnecting zone to the central zone and the at least one peripheral zonerequire substantially no polishing or blending.
 12. A corneal contactlens according to claim 10 wherein the meridional profile of theconnecting zone is described by y _(s) :=A·x ³ +B·x ² +C·x+D  (Eq. 1)with the Y value for the junction (J₁) between the central zone andconnecting zone defined by the equation $\begin{matrix}{y_{j\quad 1}:=\sqrt{r_{b}^{2} - J_{1}^{2}}} & \left( {{Eq}.\quad 2} \right)\end{matrix}$

the X value for the junction (J₂) between the connecting zone andperipheral zone defined by the equation x _(j2) :=J ₁ +W  (Eq. 3) whilethe Y value for the junction J₂ is defined by the equation y _(j2) :=y_(j1) −L  (Eq.4) with the coefficients A, B, C, D of Equation 1 aredefined by Equations 5-8 as follows: $\begin{matrix}{A:=\frac{\begin{matrix}\begin{matrix}\begin{matrix}{- \left\lbrack {{\frac{- 1}{\left( {{2 \cdot J_{1}} - {2 \cdot x_{j\quad 2}}} \right)} \cdot M} -} \right.} \\{{\frac{1}{\left\lbrack {\left( {{2 \cdot J_{1}} - {2 \cdot x_{j\quad 2}}} \right) \cdot \sqrt{r_{b}^{2} - J_{1}^{2}}} \right\rbrack} \cdot J_{1}} +} \\{{\frac{1}{\left( {J_{1}^{2} - {2 \cdot J_{1} \cdot x_{j\quad 2}} + x_{j\quad 2}^{2}} \right)}{J_{1} \cdot M}} +}\end{matrix} \\{{\frac{1}{\left( {J_{1}^{2} - {2 \cdot J_{1} \cdot x_{j\quad 2}} + x_{j\quad 2}^{2}} \right)}y_{j\quad 2}} -}\end{matrix} \\{{\frac{1}{\left( {J_{1}^{2} - {2 \cdot J_{1} \cdot x_{j\quad 2}} + x_{j\quad 2}^{2}} \right)} \cdot x_{j\quad 2} \cdot M} -} \\\left. {\frac{1}{\left( {J_{1}^{2} - {2 \cdot J_{1} \cdot x_{j\quad 2}} + x_{j\quad 2}^{2}} \right)} \cdot \sqrt{r_{b}^{2} - J_{1}^{2}}} \right\rbrack\end{matrix}}{\begin{matrix}\left\lbrack {{\frac{- 3}{\left( {{2 \cdot J_{1}} - {2 \cdot x_{j\quad 2}}} \right)} \cdot J_{1}^{2}} + {\frac{3}{\left( {{2 \cdot J_{1}} - {2 \cdot x_{j\quad 2}}} \right)} \cdot x_{j\quad 2}^{2}} +} \right. \\{{\frac{1}{\left( {J_{1}^{2} - {{2 \cdot J_{1}}x_{j\quad 2}} + x_{j\quad 2}^{2}} \right)} \cdot J_{1}^{3}} - {\frac{3}{\left( {J_{1}^{2} - {2 \cdot J_{1} \cdot x_{j\quad 2}} + x_{j\quad 2}^{2}} \right)} \cdot}} \\\left. {{J_{1} \cdot x_{j\quad 2}^{2}} + {\frac{2}{\left( {J_{1}^{2} - {2 \cdot J_{1} \cdot x_{j\quad 2}} + x_{j\quad 2}^{2}} \right)} \cdot x_{j\quad 2}^{3}}} \right\rbrack\end{matrix}}} & \left( {{Eq}.\quad 5} \right) \\{B:=\frac{\begin{matrix}{- \left( {{A \cdot J_{1}^{3}} - {3 \cdot J_{1} \cdot A \cdot x_{j\quad 2}^{2}} + {J_{1} \cdot M} + y_{j\quad 2} + {2 \cdot A \cdot x_{j\quad 2}^{3}} -} \right.} \\\left. {{x_{j\quad 2} \cdot M} - \sqrt{r_{b}^{2} - J_{1}^{2}}} \right)\end{matrix}}{\left( {J_{1}^{2} - {2 \cdot J_{1} \cdot x_{j\quad 2}} + x_{j\quad 2}^{2}} \right)}} & \left( {{Eq}.\quad 6} \right)\end{matrix}$

C:=−3·A·x _(j2) ²−2·B·x _(j2) +M  (Eq. 7) D:=y _(j2)+2·A·x _(j2) ³ +B·x_(j2) ² −x _(j2) ·M  (Eq. 8)
 13. A corneal contact lens according toclaim 1 wherein the at least one peripheral zone is formed as atruncated conoid and the relationship of the meridional profile of theat least one peripheral zone to the meridonal profile of the connectingzone is described by the angle the meridional profile the at least oneperipheral zone makes with a line perpendicular to the central axis ofthe lens.
 14. A corneal contact lens according to claim 1 wherein the atleast one peripheral zone is formed as a truncated conoid and themeridional profile of the at least one peripheral zone is described bythe angle it makes with a line perpendicular to the central axis of thelens, its curvature and its extension.
 15. A corneal contact lensaccording to claim 1 wherein the meridional profile of the at least oneperipheral zone is substantially uncurved over at least a substantialportion thereof.
 16. A corneal contact lens according to claim 1 whereinthe meridional profile of the at least one peripheral zone is terminatedby a rounded shape, to thereby provide smooth edge contour.
 17. Acorneal contact lens according to claim 1 wherein the meridional profileof the at least one peripheral zone is modeled as the quadrant of theellipse having a ellipse center on an imaginary dividing line betweenthe posterior and anterior surfaces of the lens which merges with theprofile of the at least one peripheral zone and replaces that portion ofthe meridional profile of the peripheral zone in that region beyond theintersection of the short axis of the ellipse and the profile of theperipheral zone.
 18. A corneal contact lens according to claim 17wherein the dividing line is chosen to be at a location 10 to 90% of thethickness of the lens from the posterior to the anterior surfaces andthe long axis of the ellipse chosen to be about 0.01 mm to 2.0 mm inlength.
 19. A corneal contact lens according to claim 1 wherein theanterior surface of said lens is comprised of contiguous sphericalsurfaces.
 20. A corneal contact lens according to claims 1 wherein theanterior surface of said lens is made to substantially the same shape asthe posterior surface of said contact lens.
 21. A corneal contact lensaccording to claim 1, wherein the posterior curve of said central zonein combination with the anterior surface curve will yield a desiredoptical power in said contact lens.
 22. A corneal contact lens accordingto claim 1 wherein the anterior surface of said contact lens is designedto have analogous elements to said posterior surface and said analogouselements of the anterior and posterior surfaces are equally spaced fromeach other.
 23. A corneal contact lens according to claim 1 wherein theanterior surface of said contact lens is designed to have analogouselements to said posterior surface and said analogous elements of theanterior and posterior surfaces are unequally spaced from each other.24. A corneal contact lens according to claim 1 wherein different[meridional surface profiles for each of said zones are designed atdifferent angles of rotation about the lens central axis.
 25. A contactlens comprising: a central zone having a posterior surface with acurvature; a connecting zone having a posterior surface providedadjacent and concentric to said central zone, and at least oneperipheral zone having a posterior surface provided adjacent andconcentric to said connecting zone, said peripheral zone being integralwith said connecting zone and being formed as a truncated conoid over atleast a substantial portion thereof.
 26. A contact lens according toclaim 25 wherein the meridional profile of the at least one peripheralzone is modeled as the quadrant of the ellipse having a ellipse centeron an imaginary dividing line between the posterior and anteriorsurfaces of the lens which merges with the profile of the at least oneperipheral zone and replaces that portion of the meridional profile ofthe peripheral zone in that region beyond the intersection of the shortaxis of the ellipse and the profile of the peripheral zone.
 27. Acontact lens according to claim 25 wherein the parameters of connectingzone depth and peripheral zone angle are derived by fitting lenses onthe cornea of a patient from one or more fitting sets selected from thegroup of fitting lenses having a fixed base curve and a fixed peripheralzone angle with a series of connecting zone depths, having a fixedconnecting zone depth and a fixed peripheral zone angle and a series ofbase curves, having a fixed connecting zone depth and a fixed base curvewith a series of peripheral zone angles, or sets of these three typescontain one or more lenses that are marked with a plurality of visibleconcentric rings.
 28. A contact lens according to claim 25 wherein thelens has a plurality of visible concentric rings formed over at least aportion thereof.
 29. A method of fitting a contact lens by adjusting andassessing changes to the sagittal depth of a contact lens having acentral zone with a posterior surface having a curvature correspondingin a predetermined manner to the cornea of a wearer, at least oneannular peripheral zone and an annular connecting zone, wherein changesin the axial length of the connecting zone produce directlycorresponding changes in the sagittal depth of said contact lens.
 30. Amethod of fitting a contact lens having a central zone with a posteriorsurface having a central zone with a posterior surface having acurvature corresponding in a predetermined manner to the cornea of awearer, at least one annular peripheral zone and an annular connectingzone, wherein adjusting and assessing changes to the volume distributionof a void space formed beneath the connecting zone are provided bychanging the diameter of the central zone, the axial length of theconnecting zone and/or the radial width of the connecting zone withoutotherwise affecting the fit of the lens.
 31. A method of fitting acontact lens having a central zone with a posterior surface having acentral zone having a curvature corresponding in a predetermined mannerto the cornea of a wearer, at least one annular peripheral zone and anannular connecting zone, wherein adjusting and assessing changes to theradial location of possible peripheral tangential contact of said atleast one peripheral zone to the peripheral cornea are provided bychanging the angle made by the peripheral zone to the central axis ofthe lens.
 32. A method of fitting a contact lens having a central zonewith a posterior surface having a curvature corresponding in apredetermined manner to the cornea of a wearer, at least one annularperipheral zone and an annular connecting zone, wherein adjusting andassessing changes to edge lift of said contact lens from the cornea of awearer are provided by changing the extension of the lens beyond thepoint of peripheral tangential contact of the lens with the cornea of awearer.
 33. A method of establishing centration over the visual axis ofa contact lens, comprising the steps of adjusting the location ofpossible peripheral tangential contact and extension of the lens beyondthe point of peripheral tangential contact of the lens with the cornea.34. A method of fitting, adjusting, visualizing, teaching, assessing andcommunicating a preferred geometry for a contact lens having a centralzone with a posterior surface having a curvature corresponding in apredetermined manner to the cornea of a wearer, at least one annularperipheral zone and an annular connecting zone, wherein a lens set isprovided having the central zone diameter, connecting zone width, lensdiameter and edge profile provided with predetermined shapes, andmeasuring the preferred corneal curvature needed to eliminate refractiveerror for a patient, measuring central corneal curvature of thepatient's cornea, and determining the additional parameters ofconnecting zone depth and peripheral zone angle from fitting or computermodeling to provide a contact lens to reshape the cornea in a desiredmanner.
 35. A method according to claim 34 wherein the parameters ofconnecting zone depth and peripheral zone angle are derived by fittinglenses on the cornea of a patient from one or more fitting sets selectedfrom the group of fitting lenses having a fixed base curve and a fixedperipheral zone angle with a series of connecting zone depths, having afixed connecting zone depth and a fixed peripheral zone angle and aseries of base curves, having a fixed connecting zone depth and a fixedbase curve with a series of peripheral zone angles, or sets of thesethree types contain one or more lenses that are marked with a pluralityof visible concentric rings.
 36. A method of manufacturing a contactlens that comprises: a computer system, where a specific set of dataelements comprised of parameters related to fitting a contact lenshaving a central zone, a connecting zone adjacent and concentric to saidcentral zone, and a peripheral zone adjacent and concentric to saidconnecting zone to a patients eye are input, wherein the characteristicsin each of central and peripheral zones are independent from oneanother, and said connecting zone is modeled to transition between saidcentral and peripheral zones, a system that processes said data elementsand computer lathe parameters and lens cutting data; a computerizedlathe that utilizes said lathe parameters and lens cutting data to forma contact lens that embodies the user's predetermined specifications.37. A method for altering the shape of a patients cornea comprising thesteps of: determining the desired corrected shape of a cornea, impartingforce to said cornea to alter its shape by means of a contact lenscomprising a central zone with a posterior surface curvaturecorresponding to said desired corrected shape, and a first and at leastone second annular zones concentric to said central zone, said at leastone second annular zone being positioned relative to said cornea andshaped such that upon redistribution of corneal tissue by said centralzone, said at least one second annular zone will contact said corneaacting to neutralize forces imparted on said cornea by said centralzone, and wherein said first annular zone connects said central zone tosaid at least one second annular zone.
 38. A method of treating visualacuity deficiencies by wearing a contact lens for an amount of time tomodify the shape of the cornea in a predetermined manner, comprising thesteps of: providing said lens with a central zone having a shapedesigned to impart force on said cornea, and at least one annularperipheral zone positioned relative to said central zone and shaped toselectively contact said cornea after an amount of redistribution of thecorneal tissue by said force applied by said central zone, and anannular connecting zone connecting said central zone with saidperipheral zone.
 39. A computer program product for designing a contactlens comprising: a computer usable storage medium, a computer readableprogram code means, responsive to user inputs, for modeling said contactlens to have a central zone having a posterior surface curvatureselected according to characteristics of a patient's cornea, and a firstand at least one second annular zone wherein said at least one secondannular zone is positioned and shaped to selectively engage said corneaupon alteration of its shape a predetermined amount, and said firstannular zone connecting said central zone and said at least one secondannular zone, and computer readable program code means for calculatingcutting parameters for a lathe used to produce said lens from a blank ofmaterial.
 40. The computer program product according to claim 39,wherein the first annular zone is defined by at least a parameter ofzone depth and the at least one second annular zone angle is defined byat least a parameter of it's angle relative to the cornea, wherein theseparameters are derived by calculating a best fit lens from measurementscomprising a flat keratometry reading of the patient's cornea, thepatient's refractive error, a final target refractive error, ahorizontal visible iris diameter, and a lens code relating to a lensfrom a fitting set of lenses which contacts the cornea of the patient ina predetermined manner. 41 The computer program product according toclaim 40, wherein the fitting set of lenses are selected from the groupof fitting lenses having a variable series of base curves with a fixedconnecting zone depth and a fixed peripheral zone angle, a fixed basecurve with a variable series of connecting zone depths and a fixedperipheral zone angle, variable series of base curves with a fixedconnecting zone depth and a plurality of concentric rings, a fixed basecurve with a variable series of connecting zone depths and a pluralityof concentric rings or having a fixed base curve and a fixed connectingzone depth and a series of peripheral zone angles with or without aplurality of visible concentric rings
 42. The computer program productaccording to claim 40, wherein the lens selected from the fitting lenseshas a second annular zone angle which substantially tangentially touchesthe cornea at a desired location, and the diameter of the lens at whichthe tangential touch occurs is input to model said contact lens.
 43. Thecomputer program product according to claim 42, wherein the fittinglenses have a plurality of visible concentric rings provided thereon toallow the diameter of the tangential touch to be determined.
 44. Thecomputer program product according to claim 43, wherein the angle of thesecond annular zone is calculated from the determination of diameter oftangential touch observed when fitting another fitting lens havinganother angle for the second annular zone.